Chocolate Peanut Butter Fun Cake

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*Note: I skipped the cake recipe from Bon Appetit and used another chocolate cake recipe I've made and loved before (and that is also baked in an 8X8-inch pan). If you already have a much-loved, tried-and-true 8X8-inch chocolate cake recipe, go ahead and use it. This cake simply needs a delicious chocolate base to convey the tastiness of the silky peanut butter buttercream.

*Serves 9


For the Cake:

1 1/2 cups all-purpose flour

3/4 cup granulated sugar

1/4 cup natural cocoa powder

3/4 teaspoon baking soda

1/2 teaspoon salt

1/3 cup vegetable or canola oil

1 tablespoon distilled white vinegar

1 teaspoon vanilla extract

1 cup water

For the Peanut Butter Buttercream:

1/2 cup sugar

1/4 cup egg whites (from about 2 large eggs)

1 1/2 teaspoons vanilla extract

1/4 cup creamy peanut butter

6 tablespoons (3/4 stick) chilled butter, cut into 1/4-inch cubes

1/4 cup chopped semisweet or bittersweet chocolate (about 1 3/4 ounces), for garnish

1/4 cup chopped unsalted, dry-roasted peanuts, for garnish


For the cake, adjust an oven rack to the middle position and heat the oven to 350 degrees F . Coat an 8-inch-square baking pan with nonstick cooking spray.

Whisk the flour, sugar, cocoa, baking soda, and salt together in the baking pan. Make 1 large and 2 small craters in the dry ingredients. Add the oil to the large crater and vinegar and vanilla separately to the remaining small craters. Pour the water into the pan and mix until just a few streaks of flour remain. Use a rubber spatula to spread the batter evenly in the pan if it isn’t level after mixing. Immediately put the pan in the oven.

Bake until a toothpick inserted in the center of the cake comes out with a few moist crumbs attached, about 23-25 minutes. Don’t overbake or the cake will be dry! Remove from the oven and let the cake cool completely in the pan set on a wire rack.

For the buttercream, combine the sugar and egg whites in a medium metal or glass bowl set over a saucepan of simmering water. Whisk constantly until the sugar dissolves and the mixture is hot to the touch, 3–4 minutes. Remove the bowl from off the saucepan and using an electric mixer, beat on high speed until the mixture is cool and thick, 5–6 minutes. Beat in the vanilla, then the peanut butter. With the mixer running, add butter a few pieces at a time, beating to blend between additions. Season with a pinch of salt, if desired (I didn't add any additional salt to my frosting since I used salted butter). The frosting will be much softer and less set-up than a traditional buttercream made with butter and powdered sugar. If it seems overly runny, refrigerate the frosting for an hour or so to help it firm up - but keep in mind that this isn't a frosting to pipe with, it is meant to be soft and creamy. It has the finished texture of cream whipped to soft peaks.

Run a thin knife around the cake pan to release the cake. Invert the cake onto a serving plate. Spread the peanut butter buttercream over top. Garnish with chopped chocolate and peanuts. The cake can be made and frosted up to 1 day ahead of time. Store airtight at room temperature.