Special equipment: Three 6-inch-round cake pans, an offset spatula and a bench scraper
For the cake: Preheat the oven to 350 degrees F. Coat three 6-inch-round cake pans with cooking spray.
Sift the flour, granulated sugar, cocoa powder, baking soda, baking powder and salt into a large bowl. Mix with an electric mixer at medium speed for 1 minute. Add the buttermilk, coffee, vegetable oil and eggs. Mix at medium speed for 1 minute. Scrape the side and bottom of the bowl and mix on medium speed for 1 minute more. Divide the cake batter evenly among the prepared pans. Bake on the top rack until a toothpick inserted in the center of the cakes comes out clean, about 30 minutes.
Cool the cakes in the pans for 20 minutes then turn out onto wire racks to cool completely.
For the buttercream: Add the confectioners' sugar and butter to a large mixing bowl. Beat with an electric mixer on low speed until completely incorporated, 1 to 2 minutes. Add the peanut butter, milk and salt. Mix on high speed until the mixture becomes fluffy and lighter in color, about 2 minutes. Scrape the side and bottom of the bowl and mix again on high speed for 1 minute.
To assemble the cake: Level each cake round with a serrated knife or cake leveler. Use an offset spatula to spread a thin layer of the buttercream on top of one round. Top with a second round and spread it with a thin layer of buttercream. Repeat with the third round, spreading the buttercream on the top and sides of the cake. Smooth with a bench scraper.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.