Begin by preheating your oven to 350°F (175°C). This step is crucial, as it ensures even baking.
Line a 9x13-inch baking dish with parchment paper for easy removal and cleanup.
In a mixing bowl, combine the brownie mix with the required ingredients—typically eggs, melted butter, and water. Stir until well blended, but don’t overmix. You want a fudgy texture!
Pour half of the brownie batter into the prepared baking dish. Spread it evenly across the bottom, ensuring it reaches the corners.
Spread the cookie dough over the brownie layer, covering it completely.
Pour the remaining brownie batter over the cookie dough layer and smooth it out gently.
Bake in the preheated oven for 25-30 minutes, until the edges are set and the center is slightly gooey.
Let the brownies cool in the pan for about 15 minutes, then lift them out using the parchment paper and cut into squares. Enjoy!