Prepare brownie mixture according to package instructions. Stir in Reese's Pieces candy.
Pour batter into an 8x8 or 9x9 baking dish. Bake according to the instructions on the back of the box- until brownies are set in the middle. Let cool completely before topping.
Topping
Chop each Reese's cup into 8 pieces.
Once brownies are completely cool, warm peanut butter and chocolate chips in the microwave. Stir every 20 seconds until melted. Takes about 45 seconds to 1 minute total.
Top the brownies with Reese's cups and drizzle the peanut butter chocolate mixture on top. Cut into 9 squares (or more if desired) enjoy!