Preheat a convection oven to 350°F (175°C). Grease three 8-inch round aluminum cake pans and line the bottoms with parchment paper discs.
In the bowl of a stand mixer fitted with the paddle attachment, combine sifted flour, sugar, cocoa, baking soda, baking powder, and salt. Mix on low for 30 seconds to aerate.
Add buttermilk, vegetable oil, eggs, and vanilla extract. Beat on medium speed for exactly 2 minutes to develop structure.
Reduce speed to low and gradually stream in the hot coffee. Stir by hand with a rubber spatula to ensure no dry pockets remain at the bottom of the bowl (batter will be thin).
Distribute the batter equally among the three prepared pans (approximately 450g per pan).
Bake for 30 to 35 minutes, or until the internal temperature reaches 205°F (96°C) and a cake tester inserted into the center comes out clean.
Cool cakes in the pans for 10 minutes on a wire rack before de-panning. Allow to cool completely to room temperature before frosting.
Prepare the frosting: Beat softened butter and peanut butter on medium-high for 3 minutes until pale and voluminous. Gradually add confectioners' sugar one cup at a time on low speed.
Add 1/4 cup heavy cream and vanilla. Increase speed to high and whip for 4 minutes until the texture is light and aerated.
Assemble: Place the first cake layer on a spinning turntable. Apply 1 cup of frosting and level with an offset spatula. Repeat for the second layer. Coat the exterior with a thin crumb coat and refrigerate for 20 minutes before applying the final frosting layer.
Prepare Ganache: Scald 1/3 cup heavy cream and pour over chocolate chips. Let sit for 2 minutes, then whisk from the center outward until a glossy emulsion forms. Allow to cool to 90°F (32°C).
Drip the ganache over the edges of the chilled cake using a squeeze bottle or spoon. Crown the top with mini peanut butter cups before the ganache sets.