Preheat oven to 400 degrees. Spray 12-cup muffin pan with cooking spray, or fill with paper cupcake liners.
Prepare chocolate cake mix according to package directions. Set aside.
Press 1 tablespoon of cookie dough in to the bottom of each muffin cup. Place one chocolate sandwich cookie on top of cookie dough and press down slightly. Using a tablespoon, spoon prepared brownie mix evenly over cookies. Top with one Mini Peanut Butter Cup.
Bake 18-22 minutes, or until done. Cool completely, and enjoy!