Caramelized Onion and Apple Upside Down Cake

November 4, 2021

I have a problem: I keep trying to put caramelized onions into sweets and desserts, and it keeps ending up delicious. Which just means I’ll end up doing it even more. So don’t get scared away. Trust me. Caramelized onions perfectly complement the sweet flavors in this Apple Upside Down Cake for a unique and tasty brunch, dessert, or even dinner dish.

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I was just cooking onions in a standard skillet for dinner one evening when a thought popped into my head: Why not pour cake batter over these jammy delights and call it an upside down cake? Well, it didn’t go exactly like that, but a few apple-forward adjustments created an undeniable flavor combination.

The apple slices are not only great for flavor, but they also create a beautiful visual, making this cake a perfect centerpiece for your fall and winter holidays. Plus, they are gooey, soft, and sweet from baking right up against the cast iron pan. It’s one of the best parts of this upside down cake.

What You Need to Get Started

You can easily find all of the ingredients for this caramelized onion upside down cake at your grocery store:

Let’s Make Caramelized Onions

The secret to perfect caramelized onions is patience. And butter. Their powers combine into the sweet and jammy candy of the vegetable world. In this cake, they join forces with tart apples, making for a combination that crosses multiple flavor profiles.

We’ll be making this entire cake in a cast iron pan, from caramelizing the onions, through steaming the apples, to baking the actual cake. I suggest using a well-seasoned 10-inch pan. Even if it comes pre-seasoned, you’ll have better results if you season it yourself.

Before starting the onions, combine the apples, brown sugar, and flour in a medium bowl. Toss these gently so the apples get coated, but the slices don’t snap. Set the bowl aside to let the apples marinate a bit. You’ll want your apples cut into slices that are about an eighth of an inch thick.

Then, melt the butter in your cast iron pan over medium heat. Add in the onions, and sprinkle them with some salt. Stir it all up so that the onions are coated in the butter. To cut your onions, halve and peel them. Then simply cut quarter-inch thick slices.

Allow the onions to cook, stirring occasionally, for twenty minutes or so. They should turn translucent, and then begin to darken into a golden color. Any time you notice the onions sticking to the pan or getting too browned, add a splash of water and stir to deglaze the pan.

For the next ten or fifteen minutes, stir the onions a bit more frequently. You should continue to pay attention to anything sticking to the pan, and add splashes of water as needed.

When the onions are ready, they will be very soft, medium brown, and almost jammy in texture. If you try one, it will taste sweet and nearly melt in your mouth. I recommend it. At this point, turn off the heat and transfer the onions to a bowl, leaving any leftover butter in the pan.

How to Make Apple Upside Down Cake

Now it’s time to start building the upside down cake. First, preheat your oven. Next, we’ll put the apples in the bottom of the pan, so that after the cake is done and flipped, this becomes the top. Because of that, you can have some fun with arranging the apple slices in the pan.

I styled mine in kind of a flower shape. The outer ring had slices all facing one direction, and then an inner ring I switched to face the opposite way. Start with the largest slices first to make a more balanced arrangement. If you have a few extra slices, snap them in half and fit them into any gaps.

Add a splash of water to the pan with the apples and then cover it. Cook over medium heat for just a few minutes without stirring. This will essentially steam the apples, which will help them be softer before you cover them in cake.

If you are using less firm apples, you can skip the steaming step. However, I didn’t try using anything other than granny smiths in this recipe. If needed, Pink Lady, Cortland, or Fuji apples can be used in a pinch. But I would avoid very soft or sweet apples, like McIntosh or Red Delicious.

After the apples are steamed, turn off the heat and uncover the pan. Now it’s time to put together the cake batter. This is a fairly simple batter that involves mixing wet and dry ingredients separately and then combining them.

Since there’s olive oil and no butter, you can easily do all this mixing by hand. Start with the dry ingredients in a medium mixing bowl: flour, brown sugar, salt, and baking powder. Whisk these together until they are combined. In a smaller bowl, whisk together the olive oil, cream, egg, and almond extract until it’s nice and smooth.

Pour the egg mixture and applesauce into the flour, and fold it in using a flexible spatula. For the best results, use my recipe for easy no-peel slow cooker applesauce. Using a folding motion will help you not overmix. Stir it only until just combined, and there are no visible streaks of flour. But be sure to scrape the bottom and sides of the bowl to not miss any large flour pockets.

Distribute the caramelized onions on top of the apples in the cast iron pan. These may try to stick together, so use small tongs or your hands to help spread them around evenly. Then, pour the mixed batter over the top. Use a flexible spatula to spread it into the edges, and smooth out the top.

Bake the cake for right around forty minutes. When it’s done, it will be a medium golden brown and have a spongy texture. If you gently press the center, it should bounce back. Also, a tester or toothpick will come out clean.

Set the pan on a sturdy trivet to fully cool to room temperature. To remove the cake from the pan, run the back of a butter knife around the edge. Then, place a large plate on top of the pan, and flip the whole thing over. It may take a minute for the cake to fall out, so leave the pan upside down on the plate if it doesn’t come out immediately.

This cake needs to cool fully before removing it from the pan, so be sure you give yourself enough time for that before serving. If needed, you can leave it in the pan overnight, covered tightly with foil. This will help save some time before brunch!

Luckily, it tastes great served at room temperature. If you prefer, you can microwave individual slices to warm them up slightly, but I didn’t think it was necessary.

While it tastes best the day it is cut, you can make this cake further in advance. Wrap it tightly and store at room temperature for a couple days at most. You can also store it tightly wrapped in the fridge for another couple days. You will want to microwave chilled cake to warm it up.

Caramelized onions and granny smith apples are a perfect match, especially in this Apple Upside Down Cake, that combines sweet with savory. Hello brunch!

How to Serve Onion & Apple Upside Down Cake

This spongy cake is just begging to be part of your next brunch table. For a three-course brunch, start by serving a fruit bake, like individual apple crisps to keep with the apple theme. Then serve your favorite egg dish, and finish it off with a slice of this tasty cake.

You could also include pieces of this apple upside down cake as part of a more savory dessert. Pair it with a cheeseboard, and definitely include a sharp cheddar to perfectly complements both the onion and apple flavors.

When it comes to drinks, you can’t go wrong! If you’re serving a crowd that likes to drink, try a hard apple cider sangria. Or for a mixed group, serve zero-proof or alcoholic cinnamon apple shrubs. For a tasty breakfast, try this cake alongside a chestnut cafe au lait.

Use Up Leftover Ingredients

Other Sweet & Savory Combos

Caramelized Onion and Apple Upside Cake

A moist applesauce and olive oil cake topped with a layer of super sweet caramelized onions and apple slices.
Prep Time15 mins
Cook Time1 hr 15 mins
Total Time1 hr 30 mins
Course: Breakfast, Brunch
Cuisine: American
Servings: 12 slices
Calories: 252kcal

Ingredients

Onion and Apple Topping

  • 1 Large Granny Smith Apple cut into ⅛-inch thick slices, about ½ pound apple
  • ½ Tbsp Brown sugar
  • 1 tsp Flour
  • 6 Tbsp Butter
  • 2 Large Onions sliced into ¼-inch wide half rings, about 1-1¼ pounds onion
  • ½ tsp Salt omit if using salted butter

Applesauce Cake

  • 1 ¼ Cups All-purpose flour
  • ½ Cup Brown sugar
  • ½ tsp Salt
  • 1 ½ tsp Baking Powder
  • ½ Cup Olive Oil
  • ¼ Cup Heavy Cream
  • 1 Egg
  • ½ tsp Almond Extract
  • ½ Cup Applesauce store bought or homemade

Instructions

Onion and Apple Topping

  • Combine the apples, brown sugar, and flour in a medium bowl. Toss gently to coat, without breaking the apple slices, and set aside.
  • Melt the butter in a 10-inch cast iron pan over medium heat, and then add the onions. Sprinkle with the salt, and stir to combine until the onions are coated in the butter.
  • Allow the onions to cook, stirring occasionally, for about 20-25 minutes. They should turk translucent, and then begin to darken into a golden color. Any time you notice the onions sticking to the pan or getting too browned, add a splash of water and stir to deglaze the pan.
  • For the next 10-15 minutes, stir more frequently, continuing to pay attention to anything sticking to the pan. The onions should be turning very soft, medium brown, and almost jammy in texture.
  • At this point, turn off the heat and transfer the onions to a bowl, leaving any leftover butter in the pan. Preheat the oven to 350°F with a rack in the center.
  • Give the apples one last toss, and then arrange the slices in a flower pattern in the cast iron pan. Add a splash of water, then cover the pan, and cook over medium heat for 3 minutes without stirring, to soften the apples. Turn off the heat and uncover the pan.

Applesauce Cake

  • While the apples are steaming, add the flour, brown sugar, salt, and baking powder to a large mixing bowl. Stir to combine. Mix dry ingredient and wet ingredients, then combine
  • In a smaller bowl or measuring cup, whisk together the olive oil, cream, egg, and almond extract until smooth.
  • Pour the egg mixture and applesauce into the flour, and fold in using a flexible spatula until just combined, and there are no visible streaks of flour. Be sure to scrape the bottom and sides of the bowl.
  • Distribute the caramelized onions on top of the apples in the cast iron pan. Pour the mixed batter over top, and use a flexible spatula to spread it evenly.
  • Bake the cake for 30-40 min, until it's golden brown and spongy, and a tester or toothpick comes out clean. Set the pan on a trivet to cool.
  • Let the cake fully cool in pan fully, then run the back of a butter knife around the edge. Place a large plate on top of the pan, and flip the whole thing over. It may take a minute so leave the pan upside down on the plate if the cake doesn't come out immediately.
  • Slice and serve at room temperature, or warmed in the microwave.

Notes

  • Make ahead tips:
    • The cake needs to cool fully before removing it from the pan, so be sure you give yourself enough time for that before serving. You can leave it in the pan overnight, covered tightly with foil, if needed.
    • Wrap the cake tightly and store at room temperature for 2-3 days at most. This cake tastes best the day it is cut. You can store it tightly wrapped in the fridge for another 2-3 days. Microwave individual servings to warm.
  • Homemade applesauce: Use my recipe for easy no-peel slow cooker applesauce for the rest results. 
  • Onions and apples:
    • Choose large, firm onions. I used yellow cooking onions, but sweet Spanish or Vidalia will also work well. I do not recommend red onions in this recipe.
    • Hard, tart apples, like Granny Smith work the best in this recipe. You want a baking apple that will hold its shape well and that is not too sweet. Pink Lady, Cortland, or Fuji apples can be used in a pinch.
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