Step 1: Prepare the Brownie Layer

1. Preheat the Oven: Set your oven to 350°F (175°C). Grease a 9×13-inch baking pan or line it with parchment paper for easy removal.

2. Mix Wet Ingredients: In a medium bowl, whisk together melted butter and granulated sugar until smooth. Beat in the eggs, one at a time, then stir in the vanilla extract.

3. Add Dry Ingredients: Sift cocoa powder, flour, salt, and baking powder into the bowl. Gently fold until just combined—avoid overmixing.

4. Pour and Smooth: Spread the brownie batter evenly into the prepared pan.

Step 2: Prepare the Cookie Layer

1. Cream Butter and Sugars: In a large bowl, beat the softened butter, granulated sugar, and brown sugar until light and fluffy.

2. Add Egg and Vanilla: Beat in the egg and vanilla extract until fully incorporated.

3. Mix Dry Ingredients: In a separate bowl, whisk together flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined.

4. Add Chocolate Chips: Fold in the chocolate chips evenly throughout the dough.

Step 3: Assemble and Bake

1. Layer the Cookie Dough: Drop spoonfuls of cookie dough over the brownie batter. Gently spread it out to cover as much of the surface as possible.

2. Bake: Bake for 25–30 minutes. The cookie layer should be golden brown, and a toothpick inserted into the center should come out with moist crumbs.

3. Cool Completely: Let the brookies cool in the pan for at least 30 minutes to set the layers before slicing.