Prepare the cake according to the package directions. Allow to cool 25 to 30 minutes in the pan.
Use the stick end of a wooden spoon to poke holes in the cake. In a medium bowl, whisk together the pudding mix and the Reese's creamer to make the chocolate peanut butter sauce. Allow the mixture to thicken for about 10 minutes, then pour over the cake and into the holes. *The mixture will not thicken completely to pudding consistency.
In a large bowl, whisk the peanut butter into the thawed whipped topping. Spread the frosting over the cake. Sprinkle the peanut butter cups evenly over the frosting. Cover and keep refrigerated.