If you love chocolate, peanut butter, and a beautifully bare cake, this chocolate peanut butter cake dessert filled with peanut butter buttercream, drizzled with dark chocolate sauce + peanut butter sauce, and topped with chocolate shavings is for you!
Heat oven to 350 F. Grease and line 1 8-inch round pan (at least 2 inches high) and dust the pan lightly with cocoa powder. Tap out any excess. Set aside.
In a medium bowl, combine the flour, cocoa powder, baking soda, baking powder, and salt. Stir with a whisk and set aside.
Add the dark chocolate to a small heatproof bowl and set it over a pot of barely simmering water. Stir continuously until melted and smooth. Remove from heat. Set aside to cool.
Using a stand mixer fitted with paddle attachment or a handheld mixer, beat the butter and sugar together on medium-low speed until light and fluffy. Add the eggs, one at a time, mixing well after each addition. Scrape down the sides of the bowl as needed. Add in the vanilla and the melted chocolate and mix well until well incorporated.
Set the mixer to low speed, gradually add half of the flour mixture, then the buttermilk, coffee, and then the remaining half of the flour mixture. Beat until just combined. The batter should be thick.
Pour the batter in pan. Use an offset spatula to spread the batter all the way to the edges of the pan and smooth out the surface. Bake for 30-40 minutes, or until a toothpick inserted into the center comes out with only a few dry crumbs. Cool the cake in the pan for 10 minutes, then transfer into a wire rack to cool completely.
Once cooled, peel the parchment paper off, wrap in cling film, and store in the fridge for at least 30 minutes.
Make the peanut butter sauce
Combine all the ingredients in a small sauce pan. Cook over medium heat while stirring constantly, until melted and incorporated, around 3 minutes. Once the sauce is smooth, remove from heat. Avoid cooking too long or the sauce will become very thick. Cool sauce slightly before using. (See Note 3)
Make the frosting
In a stand mixer fitted with paddle attachment or with an electric hand mixer, beat the butter on medium-high speed until smooth. Add the cream vanilla, salt, and peanut butter. Continue to beat until well incorporated.
Add 1/3 of of confectioner's sugar, beat on medium-low speed until most of the sugar has moistened. Gradually add in the remaining sugar, 1/4 cup at a time. Beat again on medium-low speed until the sugar has moistened. Turn the speed up to medium-high and beat until light and fluffy. You may need more or less confectioner's sugar depending on how soft your butter is. Scrape down the sides of the bowl as needed. (See Note 2)
Assemble the cake
Place the peanut butter buttercream in a large piping bag fitted with a large round coupler. Place the chocolate sauce and peanut butter sauce in a plastic squeeze bottle. Make some chocolate savings by using a vegetable peeler or knife to shave flat, thin shavings from a room-temperature block of chocolate.
Remove the cake from fridge and place onto a cutting surface. Split the cake into 2 even layers using a cake leveler or a bread knife. place the bottom layer onto a serving platter. Pipe big blobs of the buttercream on top of the cake. Add the second cake layer and pipe blobs of buttercream again on top.
Drizzle some peanut butter sauce and dark chocolate sauce, and then top with chocolate shavings.
Notes
(Note 1) I use this versatile dark chocolate sauce recipe. (Great for churros too!) But if you're really pressed for time, there's always store-bought chocolate sauce. ?(Note 2) When making the buttercream, do not add all the icing sugar all at once. Gradually add the sugar until you have achieved the right consistency and sweetness.(Note 3) You may have extra peanut butter sauce. To store, place in a covered container and keep in the refrigerator up to 2 weeks. Before serving, reheat in a saucepan; thin, if necessary, by adding up to 2 tablespoons cream.(Note 4) Make ahead tip: Wrap baked and cooled cake layers tightly in plastic cling wrap and store them in the refrigerator up to 2 days ahead. The frosting can be prepared, covered, and refrigerated overnight.