Inspired by the upcoming final season of Stranger Things (one of my favorite shows!), this Chocolate Upside Down Cake uses black cocoa and red plums to channel the Upside Down vibes.
I adore plums, and think they’re heavily underutilized in recipes, and I don’t know that most people would think to combine them with chocolate – but it’s surprisingly delicious.
This cake was actually my husband’s idea, and he was a genius to think it up. An Upside Down cake is perfect for a show literally dealing with the Upside Down, black cocoa for the show’s dark theme, and the overlapping red plum slices remind me of Demogorgon teeth! (and you can add slivered almonds to increase the Demogorgon-y-ness)
Why You’ll Love This Cake: It’s crazy moist, rich, and perfectly chocolatey without being too intense. There’s no frosting or icing, so you don’t need to be an expert decorator. And you don’t even need a mixer!
Serve With: My Halloween Cookies for Halloween parties, or with vanilla ice cream or whipped cream and my Salted Caramel Sauce for your Stranger Things watch party.
And if nerdy baking is your vibe, check out my Rocky Cookies, Inspired by Project Hail Mary!
The Plums
I found delicious red plums at my local farmer’s market, but any ripe plums will work just fine. There’s no need to peel the plums, as the skin cooks down so much while baking that it’s not at all noticeable.
How to Tell if Plums are Ripe?
Ripe plums will smell fruity and ‘give’ a little when gently squeezed. Don’t use underripe plums, as they won’t be as sweet and flavorful.
Can I Use a Different Fruit?
I haven’t personally tried any other fruits, but I think pears would be delicious! If you’re not a fruit person, feel free to skip the brown sugar topping and fruit entirely, and instead cover the cake with chocolate ganache (I’d use a 1:1 ratio of heavy cream to semi-sweet chocolate).
Other Important Ingredients
- The Cocoa Powder: For the full Stranger Things impact, use black cocoa powder. It can be hard to find black cocoa in stores, but it’s easily available online here.
- The Buttermilk: I highly recommend using real buttermilk here, if possible, but sour cream will work instead if needed. Do not use a ‘DIY buttermilk’ – they simply don’t work.
- The Eggs: Be sure to use large eggs, about 55 grams in shell. Do not skip the extra egg yolk. Separate your eggs when cold and allow them to come to room temp before using.
- The Chocolate: I recommend using bittersweet chocolate (I like Ghirardelli) for best results.
- The Vinegar: The white vinegar (along with the buttermilk) helps to activate the baking soda, so don’t skip it.
- The Sugar: I opted for light brown sugar, both in the topping and in the cake itself, for moisture and flavor. You can use granulated sugar instead, if needed. Note: if your brown sugar is lumpy, sift it or blitz it in a food processor before using, to avoid a lumpy cake.
- The Oil: I used vegetable oil here, but any flavorless oil should be fine. I don’t recommend using olive oil or EVOO. Be sure to give your oil a sniff before using, and don’t use it if it smells off.
- If you have struggled with dry cakes in the past, check out my How to Prevent Dry Cake post here!
The Cake Pan
I used a 9-inch (23cm) aluminum cake pan, lined with parchment paper for easy removal. Don’t use a glass or silicone pan (they don’t bake well as they can’t conduct heat evenly or efficiently), and avoid dark colored pans, as they bake too aggressively and may burn your plums.
You can use an 8-inch (20cm) pan if that’s all you have, but only if it’s at least 3-inches (7.5cm) deep, to prevent overflow – and note that it will take longer for your cake to bake. You may also need fewer plums, as it’s a smaller surface area.
How to Store Chocolate Upside Down Cake
Once completely cooled, store Upside Down Cake inside an airtight container or covered well with plastic wrap, in the fridge, for up to 4 days. I haven’t tried freezing it, but I don’t recommend it as I think the fruit on top could get weird.
More Recipes You’ll Enjoy:
- Chocolate Stout Cupcakes – similarly moist to this cake, but with delicious stout flavor!
- Chocolate Crinkle Cookies
- Dark Chocolate French Macarons
- Thick Chocolate Chip Cookies
- Nutella Stuffed Brown Butter Cookies
Chocolate Upside Down Cake
Ingredients
For the Plum Topping:
- 450-650 grams (1 – 1.7 pounds) ripe plums , about 5-7 plums
- 29 grams (2 Tablespoons) unsalted butter, cubed
- 100 grams (½ cup) light brown sugar
For the Cake:
- 113 grams (4 oz) bittersweet chocolate, chopped
- 43 grams (½ cup) black cocoa powder, or Dutch-processed cocoa works too*
- 1 teaspoon espresso powder, optional
- 115 grams (½ cup) boiling water
- 113 grams (½ cup) buttermilk**, at room temperature
- 56 grams (¼ cup + 1½ teaspoons) vegetable oil, or any flavorless oil
- 2 large eggs + 1 extra yolk, separated when cold and brought to room temperature
- ½ teaspoon white vinegar
- 1 Tablespoon vanilla extract
- 200 grams (1 cup) light brown sugar, sifted if lumpy
- 97 grams (¾ cup) all-purpose flour
- ½ teaspoon baking soda
- ½ teaspoon salt
Instructions
Prepare the Topping:
- Prepare a 9×2-inch (23x5cm) cake pan by spraying with cooking spray and lining with parchment paper on the base and sides of the pan. Set aside.
- Slice the plums into approximately ¼-inch (0.6cm) slices. Try to keep the slices an equal thickness.
- In a small skillet or saucepan, melt the butter and 100g brown sugar together until melted and combined. Transfer to prepared cake pan, spreading across the base evenly.
- Arrange the sliced plums across the base, placing in concentric circles with the slices overlapping slightly (or in more of a flower pattern, for the Demogorgon look). Set aside.
Make the Cake:
- Preheat oven to 350°F / 175°C.
- In a small heatproof bowl, place the chopped chocolate, black cocoa powder, and espresso powder (if using). Pour the boiling water over the top and cover. Set aside for 5 minutes, then whisk until smooth. Set aside to cool until it's about room temperature (set in the fridge if needed).
- In a large bowl, combine the buttermilk, oil, eggs, egg yolk, vinegar, and vanilla. Whisk to combine.
- Once the chocolate mixture has cooled, add this to the egg mixture, whisking to combine. Use a rubber spatula to scrape down the sides of the bowl.
- Add brown sugar, flour, baking soda, and salt. Use a rubber spatula to combine, ensuring the sides and bottom of the bowl are incorporated too. Do not overmix.
- Pour the cake batter over the top of the arranged plums. Tap the cake pan firmly on the countertop a few times, to release any air bubbles.
- Bake for 40 – 50 minutes, or until the cake is set and a toothpick inserted in the center comes out with just a few moist crumbs.
- Place cake pan on a wire rack and allow to cool for 30 minutes before inverting on to a cake platter. Serve with vanilla ice cream, whipped cream, or by itself. Serve warm or cool (it's delicious both ways!).
