Preheat oven to 350 degrees. Lightly grease a 9x13 inch pan with cooking spray.

Prepare the chocolate fudge brownie batter according the directions on the package. Spread the batter in an even layer in the pan. Set aside.

Beat the cream cheese in a large bowl with an electric mixer until fluffy. Pour in sweetened condensed milk and peanut butter, beating until smooth. Fold in Reese's Pieces. Pour the mixture over the brownie batter and spread carefully in an even layer.

Bake for 40 minutes, until the top layer is set and golden brown on the edges. Cool for 30 minutes in the refrigerator.

In a small microwavable bowl, combine chocolate chips and whipping cream. Microwave on high for 1 minute and stir to combine. If the chips aren't melted, microwave an additional 30 seconds. Spread over the top layer. Sprinkle over the chopped Reese's Peanut Butter Cups and refrigerate until the top layer is set.