**Prepare the Brownie Batter**
1. Mix the Brownie Base: Follow the package directions for your brownie mix, combining it with the required oil and egg in a medium bowl, stirring until just combined. The batter should be smooth with no lumps remaining, taking about 2 minutes of mixing.
2. Prepare the Pans: Line a 12-cup muffin tin with paper liners or grease each cup lightly. Divide the brownie batter evenly among the cups, filling each about halfway up the sides, using roughly 2 tablespoons per cup.
**Build the Brookie Layers**
1. Add the Peanut Butter Cup: Press one Reese's cup into the center of each brownie batter cup, pushing it down so it sits partially submerged but not completely covered.
2. Top with Cookie Dough: Tear off pieces of refrigerated cookie dough and flatten them slightly, then place one piece over each peanut butter cup, covering it completely and sealing the edges to the brownie batter below, using about 2 tablespoons of dough per cup.
**Bake to Perfection**
1. Preheat and Bake: Preheat your oven to 350 degrees Fahrenheit. Place the filled muffin tin in the oven and bake for 22 to 26 minutes, until the cookie dough layer is golden brown but still slightly soft in the centers when gently pressed.
2. Cool Briefly: Allow the brookies to cool in the muffin tin for 5 minutes before carefully removing them, which allows the chocolate inside to set slightly but keeps them warm for serving.