Start by making Hershey's Perfectly Chocolate Chocolate Cake. After the layers have cooled, put them on separate plates, cover with plastic wrap and freeze until solid (at least 2 hours).
Peanut Butter Mousse Filling
Mix together:
3/4 cup creamy peanut butter
5 ounces cream cheese, softened
2 tablespoons butter, softened
1 1/4 cups powdered sugar
Once they are well combined, fold in one 8 ounce container of whipped topping (cool whip :)
After the cakes are frozen, pull one layer out of the freezer and spread the peanut butter mousse filling over the top; carefully place back into the freezer (uncovered) and freeze until fairly solid (at least 1 hour). Then remove from the freezer and place the top layer of cake onto the mousse covered layer. Frost the tops and sides with Hershey's Perfectly Chocolate Chocolate Frosting.
Cut Reese's Peanut Butter Cups in half and decorate the top. Keep cake in the freezer. Let sit at room temperature for 5-10 minutes before cutting and serving.
