Preheat oven to 350 degrees. Grease and flour 2 round 9-inch cake pans.
For the cake, put flour, sugar, cocoa, baking powder, baking soda and salt in a bowl and mix well.
In a stand mixer, mix the buttermilk, oil, eggs, vanilla together. Slowly add in the mix of dry ingredients while the mixer is on low. Add the coffee and make sure everything is combined. The batter will be very thin.
Pour the batter into the prepared pans and bake for about 25 minutes or until a toothpick inserted in the middle comes out clean.
Turn the cakes out onto a cooling rack. While the cakes are cooling, make your frostings.
Peanut Butter Frosting:
In a bowl, blend together peanut butter, powdered sugar, butter, and milk 3-4 minutes or until light and fluffy.
In a stand mixer with the beater blade, beat the butter for 1-2 minutes until it is smooth, creamy and nearly white in appearance.
Add in the salt and vanilla. Mix until incorporated.
With the mixer on low speed, slowly add in the powdered sugar and cocoa powder.
Add the heavy cream, a tablespoon at a time, mixing slowly until it is the consistency that you'd like.
Beat for 1 minute on medium speed until smooth and creamy.
Assemble The Cake:
Frost the top of the first cake with the Peanut Butter Frosting. Then layer the other half of the cake on top. Frost the outside of the cake with the Chocolate Buttercream Frosting.
Pipe flowers on top with the leftover Peanut Butter Frosting and/or decorate as desired with chopped Reese's Peanut Butter Cups.
The calories shown are based on the cake being cut into 15 pieces, with 1 serving being 1 slice of cake and using all of the frosting on the cake. If you'd like to lower the calories, use less frosting and make a "naked" style cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate.