Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round baking pans to ensure easy removal of the cakes later.
In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt until well combined.
In another bowl, mix the eggs, buttermilk, hot coffee, vegetable oil, and vanilla extract. Whisk until smooth.
Gradually add the wet mixture to the dry ingredients, stirring until just combined. Be careful not to overmix; a few lumps are okay.
Divide the batter evenly between the prepared pans. Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean. Let them cool in the pans for about 10 minutes before transferring to a cooling rack.
While the cakes cool, it’s time to make the peanut butter frosting. In a large bowl, beat together the creamy peanut butter, unsalted butter, powdered sugar, heavy cream, vanilla extract, and kosher salt until smooth and fluffy.
Heat 1 cup of heavy cream in a saucepan until just simmering. Pour it over the chopped semisweet chocolate and let it sit for a few minutes before stirring until smooth.
Once the cakes are completely cool, place one layer on a serving plate. Spread a generous layer of peanut butter frosting over the top and sprinkle half of the chopped peanut butter cups. Place the second layer on top.
Spread the remaining peanut butter frosting over the top and sides of the cake. Drizzle the chocolate ganache over the top, allowing it to drip down the sides. Finally, garnish with the remaining chopped peanut butter cups.
