CAKE: Preheat oven to 350 degrees F. Grease three 8-inch round cake pans, lining the bottoms with parchment paper. Grease the parchment paper and sides; set aside.
In a large bowl, sift together the flour, sugar, cocoa powder, baking soda, baking powder and salt. In a medium bowl, whisk together the eggs, buttermilk, coffee, oil and vanilla.
Add the wet ingredients to the dry ingredients, mixing for 2-3 minutes.
Divide the batter evenly between the 2 pans. Bake for 20 minutes. Continue to bake until a toothpick inserted into the center of one of the cakes comes out almost clean (with a few moist crumbs), about 12 more minutes.
Cool the cakes for 15 minutes; carefully turn them out onto cooling racks to completely cool.
If the cakes baked have a domed top, level off the tops with a knife. Place one cake layer on a serving plate. Cover with 1 cup of the peanut butter frosting and sprinkle 10 of the chopped peanut butter cups over the frosting.
Place on top the second cake layer and cover with another 1 cup of the peanut butter frosting, with 10 chopped peanut butter cups.
Place the final cake layer on top face-down (flat edge facing up), and frost with the remaining peanut butter frosting, finishing it as smoothly as possible.
Refrigerate the cake for at least 1 hour, until the frosting is set.
PEANUT BUTTER FROSTING: In a large bowl add the powdered sugar, peanut butter, butter, vanilla and salt; mix on medium-low speed until creamy. Add the heavy cream and beat on high speed, until the mixture is light and smooth.
CHOCOLATE GANACHE: Chop the chocolate into small pieces so it will melt easily and evenly, and place in a small bowl. Place the cream in a small saucepan over medium heat and warm until it just comes to a boil.
Pour the nearly boiled cream over the chocoalte and allow to sit for a couple of minutes; stir until melted and smooth.
Set aside to cool, whisking occasionally, until it has thickened slightly, but not firm (you want it pourable over the cake).
Pour the chocolate ganache into the center of the cake, letting it run over the sides of the cake. Top with the remaining 10 chopped peanut butter cups.
SERVING: Refrigerate the cake before serving, allowing the ganache a chance to set up. Slice and serve!