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 well 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 stand mixer with the beater blade attachment, blend together the butter, peanut butter, powdered sugar, and 6 tablespoons heavy cream. While the mixture is beating on low speed, add in additional tablespoons of heavy cream if needed to get a spreadable consistency. Beat the frosting on medium-low speed for 1-2 minutes. This frosting will be thick, but should lighten up a bit after beating.
Make the Chocolate Buttercream .
Now it's time to put your cake together!
Frost the top of the first cake with a thin layer of peanut butter frosting. Put about 1/2 of the chopped Snickers bars on top of the peanut butter frosting. Then layer the other half of the cake on top. Frost the outside of the cake with the remaining peanut butter frosting, smoothing as much as possible, but it doesn't have to look perfect!
Spoon the chocolate buttercream into a decorating bag with Wilton tip 2D. Pipe stars on the top outer edge and around the bottom.
Sprinkle the remaining candy bar pieces on the top of the cake.
This cake can be made a day in advance. It is OK to leave sitting at room temperature for about a day, but if you are keeping it longer than a day, cover the cake and refrigerate it.
The calories shown are based on using all of the icing and the cake being cut into 15 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate.