Preheat oven to 350°F (175°C). Line a 7x11 inch baking pan with parchment paper, allowing the paper to overhang the sides for easy removal.

Prepare the peanut butter cookie dough according to the package directions. Stir in 1/4 cup of Reese's Pieces.

Prepare the brownie batter according to the package directions. Pour the brownie batter into the prepared baking pan and spread evenly.

Drop spoonfuls of the peanut butter cookie dough over the brownie batter. Lightly press them down so they are partially submerged.

Sprinkle additional Reese's Pieces over the cookie dough, if desired.

Bake for 30-35 minutes, or until the cookie topping is golden brown and a toothpick inserted into the brownie section comes out clean.

Let the brookies cool completely in the pan on a wire rack before cutting into squares.