Rich chocolate cake layers with creamy peanut butter buttercream, chocolate ganache, and peanut butter cups
Preheat the oven to 350 °F. Spray three 6-inch round cake pans or two 8-inch round cake pans with non-stick spray, line the bottom of each pan with parchment paper and spray again. Set aside.
In the stand mixer bowl fitted with a paddle attachment, stir together the all-purpose flour, cocoa powder, granulated sugar, baking soda, and salt. Set aside.
Add the eggs and the vegetable oil on low until well incorporated.
Pour in the buttermilk and add brewed coffee. Mix on medium for 30 seconds. Scrape down the sides of the bowl.
Evenly distribute the cake batter among the three cake pans and bake for about 35-40 minutes or until a toothpick inserted into the center of each cake comes out clean or with just a few moist crumbs.
Remove cakes from the oven and let cool in pans for 10 minutes before inverting onto cooling racks to cool completely — wrap cakes in plastic wrap and place in the freezer to chill for 30 minutes.
Add semi-sweet chocolate chips to a small microwavable bowl. In another small microwavable bowl, heat the heavy cream to a light simmer for about 1 minute.
Pour hot, heavy cream over chocolate chips. Allow chocolate to melt for 1 minute. Use a whisk or rubber spatula to mix the chocolate and cream. Mix until its velvety smooth. If chocolate is still not melted, heat in the microwave in 15-second increments.
In the stand mixer bowl fitted with the paddle attachment, beat the butter and peanut butter until light and fluffy, about 2 minutes.
Turn the mixer to low and add the salt and vanilla.
Next, gradually add powdered sugar, followed by the cream. Mix on medium-high speed for about 5 minutes, until light and fluffy. Scrape down the sides of the bowl. Add more heavy cream if the buttercream looks dry.
Before using, turn the mixer on low and mix for 2 minutes to push out any air bubbles or use a rubber spatula to push out the air bubbles. (You will need to repeat this step when frosting the outside of the cake and add more heavy cream if buttercream looks dry).
Remove the chocolate cake layers from the freezer and unwrap the cake layers. Next, use a serrated knife to cut off the dome of the cakes to make the layers flat and even.
Add a small amount of buttercream onto the center of the cake board.
Layer a chilled chocolate cake, cut side up onto the cake board. Pipe ⅔ cup of buttercream on top of the cake and use an offset spatula to smooth it out.
Drizzle chocolate ganache over the top.
Place another cake layer cut side down over the top. Repeat the process for another layer—Crumb coat and freeze for 30 minutes. (Check buttercream consistency and re-whip as needed).
On the chilled cake, add a thicker layer of buttercream all around the cake. Then use the offset spatula and cake scraper to smooth the sides.
Starting from the bottom of the cake, hold the offset spatula perpendicular to the board and slowly move the spatula up the sides of the cake as you are spinning the turntable. Continue to make rustic texture lines up the sides of the cake and smooth the top of the cake.
Drizzle chocolate ganache on top of the cake in a grid-like pattern.
Pipe a round swirl, then place a peanut butter cup next to it and pipe another round swirl, continue this pattern around the cake.
Serve at room temperature and enjoy!