Preheat oven to 350°F. Spray a 9x13-inch baking dish with nonstick cooking spray.
Prepare the brownie mix according to the package directions. My mix called for eggs, water, and melted butter.
Pour the brownie batter into the prepared baking dish and spread evenly.
Place the pre-formed cookie dough pieces throughout the brownie batter, leaving a little space between each piece. Gently press the dough slightly into the brownie batter.
Bake at 350°F for 30–45 minutes, checking around the 30-minute mark. The edges should be set and the cookie dough should be golden brown.
During the final few minutes of baking, break the chocolate bar into pieces and scatter them over the top.
Return the pan to the oven for a few minutes, just until the chocolate softens and melts slightly.
Remove from the oven and allow the brookies to cool before slicing.
Cut into squares and serve warm or at room temperature.
