Preheat the oven to 350°F (175°C). Lightly grease a 12-cup muffin tin with nonstick cooking spray.
Divide the chocolate chip cookie dough into 12 equal portions. Press one portion evenly into the bottom of each muffin cup to form a cookie base.
Place one Reese’s Peanut Butter Cup, upside down, in the center of each cookie dough layer.
Carefully spoon the prepared brownie batter over the peanut butter cups, filling each muffin cup almost to the top.
Bake for 20–25 minutes, or until the brownie tops are set and a toothpick inserted near the edge comes out mostly clean.
Remove the muffin tin from the oven and allow the brookies to cool completely before removing them from the pan to prevent breaking.
Serve and enjoy these rich, peanut-butter-filled brownie-cookie treats!
Enjoy!