Rhubarb Cake with Creamy Rhubarb Jam and Buttercream
May 20, 2021
When a friend stopped by for a visit recently with a bag full of rhubarb, I wasn’t quite sure what I was going to do with it. After tossing around a few ideas, I landed on this sweet and springy rhubarb cake. The simple flavors allow this vegetable to shine, focusing on balancing its tart flavor with sugary sweetness.
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If you are not able to grow your own fruits and veggies, get yourself a friend with the extra land to do so. Or find a local farm to buy from. Rhubarb is one of those plants that grows in abundance where I live, and so there is plenty to use when it’s in season.
It’s an interesting plant. The leaves are poisonous, and the stalks look kind of like a reddish celery. But the flavor is tart, and when cooked, it breaks down into a mush that is perfect for baked goods. You’ve probably enjoyed it alongside strawberries, or other sweet fruit. Here, it is the star, accented only by sweet vanilla.
What You Need to Get Started
You can easily find all of the ingredients for this sweet and tangy rhubarb cake at your grocery store:
- Pantry: Flour, Cornstarch, Sugar, Baking powder, Baking soda, Confectioner’s sugar, Gel food coloring
- Spice Rack: Salt, Vanilla extract, Sea salt
- Fridge: Butter, Milk, Eggs, Heavy cream
- Produce: Rhubarb
- Required Equipment: 9×13 baking pan, Parchment paper, Stand mixer, Silicone spatula, Cooling rack, Saucepan
- Optional Equipment: Sifter or mesh strainer, Cake leveler, Piping bag, Turn table, Mini offset spatula
Let’s Make Rhubarb Cake
The cake recipe I use here is based off one from Sally’s Baking Addiction, and uses an interesting technique called reverse creaming. This results in a springy cake with a soft crumb and a buttery, vanilla flavor. With a few adjustments, it’s the perfect backdrop for highlighting rhubarb.
Before you begin to mix up the batter, preheat your oven with a rack in the center. Line a baking pan with parchment paper. To get it to fit nicely without any wrinkles, cut diagonally in from the corners and create an overlap. Grease the paper and then set the pan aside.
To get started, you will actually be combining all of the dry ingredients in your mixer bowl first. This probably feels backwards from the standard method of making cakes where you cream butter and sugar. However, this “reverse creaming” helps with the texture of the cake.
Sift together the flour, cornstarch, sugar, baking powder, baking soda, and salt. If you don’t have a true sifter, that’s okay. You can always shake the ingredients through a fine mesh strainer to help remove any lumps or large pieces. Pulse your mixer on low for a few short bursts to combine everything together.
Add in the butter, vanilla, and half the milk and mix together on medium low for just about a minute. For the best results, cube butter that is cold from the fridge, and then leave it out at room temperature to warm up. It’s easier to cut cold, but needs to be thawed to mix into the cake well.
Your milk should also be room temperature, since having all your ingredients the same temperature helps them come together. When this step is done, the butter will be incorporated into the flour, and all the dry ingredients will be moist. The texture should be similar to a pie crust dough.
To make the smooth cake batter that we’re all used to, add in the rest of the milk along with eggs and Greek yogurt – you guessed it, also at room temperature. Use your mixer on medium low just until everything is combined together.
Stop every ten to fifteen seconds and use a silicone spatula to scrape the batter down off the sides of the bowl. The total mixing time should be only about a minute, so you don’t end up over mixing. It’s okay if there are a few lumps, but there should not be any obvious dry pockets or streaks.
Discard any rhubarb leaves and trim the ends. If the red skin on your stalks is particularly tough, you may choose to peel it off, but it’s not required. Roughly chop the rhubarb into about quarter to half inch pieces.
Add these into the batter, and combine with a silicone spatula. You want to use a folding motion, where you scrape along the sides and bottom of the bowl and then flip the batter over on top of the rhubarb. This helps incorporate the tart vegetable without mixing too much.
Transfer the batter to your prepared baking pan, and smooth it out with your spatula. Get in that bowl and scrape all the good stuff off the edges and bottom, so you don’t miss out on any cake.
Bake the cake for for just around forty minutes. If you know your oven runs hot, start checking it a bit early to see if it is done. When the cake is ready, it will have a light golden color on the top, darker toward the edges.
A toothpick may come out clean before the center is fully cooked. You can double check doneness by gently pressing on the center of the cake with your fingertip. If it bounces back, it’s done. If not, continue baking.
Once it’s ready, remove the cake from the oven and place the pan on a wire rack to cool completely to room temperature. You don’t want to work with the cake while it’s still warm at all. If you are finishing this later, store the unfrosted cake covered at room temperature for a couple days, or freeze for a couple months.
How to Fill Rhubarb Cakes
While the cake is cooling, it’s time to make the filling. Since we will be making this big sheet cake into little mini round layer cakes, you’ll want something to go between those layers. Enter creamy rhubarb jam, which you can quickly make on the stove.
Begin by melting the butter in a saucepan over medium heat. Add in some more chopped rhubarb and sugar. You can prepare the rhubarb exactly as you did for the cake.
Cook, stirring the mixture occasionally as the rhubarb begins to soften and release its liquid thanks to the help of the sugar. After a few minutes, the water will begin to cook off, and the rhubarb will break down into a tasty mush. After just under ten minutes, when it has thickened somewhat, turn of the heat.
Stir in the heavy cream and a pinch of salt to taste. Transfer the filling to a pint-sized mason jar, since this makes just a bit too much for the smaller half-pint jars. Cover it loosely with the lid, and allow the jam to cool down to room temperature.
If you are using it immediately, you can leave it out at room temperature until the cake is also cooled and ready. To make this in advance, seal the jar tightly and store it in the fridge for a couple days. You can use it on the cake cold or at room temperature.
To make the mini cakes, you will need a cookie cutter or biscuit cutter that is about four inches in diameter. This is the perfect size to make six cakes, and have plenty of extra crumbs left over for the topping. If you have a smaller cutter, do some quick eyeballed measurements to see how many cakes you can fit before cutting them out.
Remove the cake from the pan carefully, using the parchment paper. I found it easier to do this with four hands, so grab a friend if you are able. Lift the completely cooled cake out of the pan and place it onto a work surface. Cut out your cake circles and place any scraps in a bowl off to the side.
Using a cake leveler or serrated knife, cut each round cake into two vertical layers. If using a knife, keep the cakes flat on your work surface, and hold the knife horizontal, parallel to the table. Try to keep it as steady as possible for the most evenly cut layers.
These will be a bit uneven on top as well, since the middle of the cake may be slightly mounded. If you’d like, you can cut the very top off to flatten that out as well, which may make for a prettier final product. I’m a bit of a lazy baker, so I didn’t bother.
Add a couple spoonfuls of the creamy rhubarb jam filling onto the bottom layer of each cake, and spread it around evenly. Then top with the other half, like a delicious cake sandwich. Place the cakes back in the pan and cover, or on a couple plates, and chill them in the fridge for an hour.
Meanwhile, grab that bowl of the cake scraps, and use your hands or a fork to break down the pieces into smaller crumbles. Cover the bowl and let it sit aside at room temperature while the cakes chill and you prepare the buttercream frosting.
Finish and Decorate Rhubarb Cakes
Because rhubarb tends to be quite tart, I decided to allow the natural sweetness of a traditional American buttercream balance that out. Luckily, it’s one of the easiest frostings you can make, and only requires three ingredients.
In the bowl of your stand mixer, add in room-temperature butter and whip on medium speed until visibly lightened in color and fluffy. Then add in the sugar a cup at a time. Completely incorporate each cup before adding the next, and stop after mixing in each to scrape down the sides of the bowl.
You will need to add the milk a little bit at a time to achieve your desired consistency, depending on whether you will be piping it or spreading it onto the cakes. Piping frosting will require it to be slightly less stiff. At the end, add any food coloring you would like and mix it until it’s fully incorporated.
To get this bright pink color, I used just a single drop of red gel and also dipped the tip of a toothpick into blue to add just the tiniest bit. Transfer the icing to a piping bag if desired. No tip is needed, since you’re mostly using the bag to get the frosting on the cake, rather than decorating.
Remove the cakes from the fridge and place one on a turntable, cake stand, or other flat surface that you can work around or spin. I used a small upside-down bowl on top of a plate, so I could get into the bottom edges of the cakes, and easily spin them around.
Pipe some frosting around the sides and on top of the cake. There’s no need to full cover every surface, since you can spread it and always add more. Use a mini offset spatula or butter knife to spread the frosting all over the cake.
Scrape off any excess, and then repeat the frosting process for the rest of the cakes. Grab that bowl of cake crumbs you set aside earlier, and top each cake with the a handful of them, pressing to adhere the crumbs to the frosting.
You can make the buttercream frosting up a few days in advance and store in the fridge. Let it thaw to room temperature before working with it. You may also need to re-whip it in your mixer with another splash of milk if it’s too thick.
The fully decorated cakes can be stored in the fridge for a few days, Or you can wrap them tightly in plastic wrap and then foil, and freeze for a few months. Thaw frozen cakes in the fridge overnight before serving them. The finished cake can be served directly from the fridge or after warming it up to room temperature. It’s delicious either way.
If you end up with some leftover cake scraps, creamy rhubarb jam, or even buttercream, you can combine them all together and eat them as a snack. Or form the mixture into balls and dip in melted white chocolate to make cake pops or truffles!
Tart rhubarb is balanced with sweet vanilla cake and buttercream in these adorable mini cakes, perfect for spring!
How to Serve Mini Rhubarb Cakes
These mini cakes are adorable to display on a dessert table, but they are definitely not bite-sized! I suggest cutting each into quarters to serve for a fairly standard-sized slice of cake. The good news is that everyone gets a corner with lots of buttercream.
Because the cakes freeze well, they make great desserts to have on hand for a special occasion. Try celebrating a small family birthday with a slice and some colorful birthday cake martinis. Or during the summer, serve with some decaf cold brew coffee.
You can always serve these as snacking cakes or steal a slice for breakfast. I’m thinking of building an entire brunch around these, and serving a strawberry caprese salad or a chicken caesar pasta salad to balance out the sweetness. Don’t forget a refreshing watermelon daiquiri to keep with the color theme.
Use Up Leftover Ingredients
- Extra rhubarb pairs with its longtime friend in a classic strawberry rhubarb crumble.
- Add Greek yogurt for extra moist baked treats, like a butternut squash curry cornbread.
- Your baking basics like flour, butter, eggs, and sugar can be used in plenty of cake and cookie recipes. Try lemon curd sandwich cookies for something fresh and fun.
Rhubarb Cake with Creamy Rhubarb Jam and Buttercream
- 2 ¾ Cups Flour
- ¼ Cups Cornstarch
- 1 ½ Cups Granulated Sugar
- 1 tsp Baking Powder
- ½ tsp Baking Soda
- ½ tsp Salt
- 1 cup Unsalted Butter cubed and room temperature
- 1 Tbsp Vanilla extract
- 1 Cup Milk room temperature, divided
- 3 Eggs room temperature
- ½ Cup Greek Yogurt room temperature
- 1 ½ Cups Rhubarb trimmed and roughly chopped
Creamy Rhubarb Jam
- 2 Tbsp Butter
- 1 ½ Cup Rhubarb trimmed and roughly chopped
- ½ Cup Sugar
- ¼ Cup Heavy Cream
- pinch Sea Salt
- 1 Cup Unsalted Butter room temperature
- 3 Cups Confectioner's Sugar
- 2-4 Tbsp Milk
Bake the Rhubarb Cake
- Preheat the oven to 350°F with a rack in the center. Line a 9x13 baking pan with parchment paper and grease the paper.
- In the bowl of a stand mixer fitted with the paddle attachment, sift together the flour, cornstarch, sugar, baking powder, baking soda, and salt. Mix on low for a few short bursts to combine.
- Add in the butter, vanilla, and half the milk and mix together on medium low until the butter is incorporated into the flour mixture and everything is moist, about 1 minute. The texture should be similar to a pie crust dough.
- Then add in the eggs, yogurt, and remaining milk. Mix just until everything is combined, stopping every few seconds to scrape down the sides of the bowl with a silicone spatula. Total mixing time should be about 1 minute.
- Fold in the rhubarb pieces with a silicone spatula and then transfer the batter to the prepared baking pan.
- Bake the cake for 35-45 minutes, checking a bit early to see if it is done. A toothpick may come out clean before the center is fully cooked. Double check by gently pressing on the cake. If it bounces back, it's done. If not, continue baking.
- Allow the baked cake to cool completely in the pan on a wire rack.
Make the Creamy Rhubarb Jam Filling
- While the cake is cooling, melt the butter in a medium saucepan over medium heat. Then add in the rhubarb and sugar. Cook, stirring occasionally as the rhubarb begins to softened and form into a thick jam-like texture, about 8-10 minutes.
- Turn off the heat and stir in the heavy cream. Transfer the filling to a jar. Cover loosely and allow to cool to room temperature. Then seal and store in the fridge for 1-2 days if needed.
- Carefully use the parchment paper (and a friend if needed) to lift the completely cooled cake out of the pan and onto a work surface. Using 4-inch diameter round cookie or biscuit cutters, cut out 6 circles of cake. Place the scraps in a bowl and set aside.
- Using a cake leveler or serrated knife, cut each round cake into two vertical layers. Spread 1-2 tablespoons of the filling on the bottom half of each cake, and top with the other half. Chill the cakes in the fridge for an hour.
- Break down the cake scraps into crumbles. Cover and let sit aside at room temperature while the cakes chill and you prepare the frosting.
Make the Buttercream and Decorate
- In the bowl of a stand mixer fitted with the paddle attachment, add the butter and whip on medium speed until visibly lightened in color and fluffy, about 1-2 minutes.
- Add in the sugar 1 cup at a time and completely incorporate each cup before adding the next. Stop to scrape down the sides of the bowl in between.
- Add the milk as needed to achieve your desired texture. Piping frosting will require it slightly less stiff than if you are spreading. Add any food coloring you would like and mix to incorporate. I used 1 drop of red gel and a toothpick dipped in blue gel for this bright pink color. Transfer the icing to a piping bag with no tip if desired.
- Remove the cakes from the fridge and place one on a turntable, cake stand, or other flat surface that you can work around or spin. Pipe frosting around the sides and on top of the cake, and then spread using a mini offset spatula or butter knife. Scrape of any excess and repeat for the rest of the cakes.
- Top each cake with the leftover cake crumbles. Cut in quarters to serve immediately, or store for later.
- Make ahead tips:
- Store the unfrosted cake covered at room temperature for 1-2 days. The unfrosted cake can be tightly wrapped and frozen for 2-3 months. Thaw in the fridge overnight before decorating.
- The creamy rhubarb jam can be sealed and stored in the fridge for 1-2 days, once cooled to room temperature.
- Make buttercream frosting up to 2-3 days in advance and store in the fridge. Let it thaw to room temperature before using. You may need to remix it with another splash of milk if too thick.
- Decorated cakes can be stored in the fridge for 2-3 days or wrapped tightly and frozen for 2-3 months. Thaw in the fridge overnight before eating. The finished cake can be served directly from the fridge or after warming to room temperature.
- If you end up with leftover cake scraps, creamy rhubarb jam, and/or buttercream, combine them all together in a bowl and dip in melted white chocolate to make cake pops!