Step 1: Prepare Your Pan
Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal. Lightly spray with cooking spray.

Step 2: Make the Brownie Batter
In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth. Add the cocoa powder and whisk until no lumps remain. Add eggs and vanilla, whisking until the mixture is glossy and well combined. Gently fold in the flour and salt just until incorporated. Don’t overmix! Set aside.

Step 3: Prepare the Cookie Dough
In a separate large bowl, cream together the softened butter, granulated sugar, and brown sugar using an electric mixer on medium speed for 2-3 minutes until light and fluffy. Beat in the egg and vanilla until smooth.

Step 4: Combine Cookie Dry Ingredients
In a medium bowl, whisk together flour, baking soda, and salt. Add to the butter mixture and mix on low speed just until combined. Fold in the chocolate chips with a spatula.

Step 5: Layer in the Pan
Spread the brownie batter evenly across the bottom of your prepared pan. Drop spoonfuls of cookie dough over the brownie layer, then gently spread it out to cover as much surface as possible. Don’t worry if you can’t cover every spot perfectly – a little brownie peeking through is fine and creates a beautiful marbled effect.

Step 6: Bake
Bake for 32-37 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs (not wet batter). The cookie top should be golden brown. The center may look slightly underdone, but it will continue cooking as it cools.

Step 7: Cool Completely
Let the brookies cool in the pan on a cooling rack for at least 30 minutes, then use the parchment overhang to lift them out. Let cool completely before cutting – this ensures clean cuts and prevents crumbling.

Step 8: Cut and Serve
Using a sharp knife, cut into 16-20 squares. Wipe your knife clean between cuts for the neatest edges. Serve and watch them disappear!