Bake chocolate cake per box instructions. Allow them to cool and set aside until you are ready to frost.
Frosting
To make the frosting, combine butter, peanut butter, and brown sugar. Mix until creamy and smooth. Fold in powdered sugar, in two parts then add in heavy cream.
Mix until creamy and smooth. After cupcakes have cooled frost cupcakes and top with payday crumbles. Serve immediately or refrigerate until ready to eat.