01 - Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a medium bowl, whisk the melted butter and granulated sugar until well combined. Add the eggs and vanilla extract, whisking until the mixture is smooth and glossy. Fold in the flour, cocoa powder, and salt using a spatula, mixing until just incorporated. Spread the batter evenly across the bottom of the prepared pan.
03 - In a separate bowl, beat the softened butter, brown sugar, and granulated sugar with an electric mixer until light and creamy, about 2 minutes. Add the egg and vanilla extract, mixing until fully incorporated. In another bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, stirring until just combined. Fold in the chocolate chips.
04 - Drop spoonfuls of the cookie dough evenly over the brownie batter. Gently spread with a spatula to create an even top layer — it is perfectly fine if some brownie batter peeks through.
05 - Bake for 28 to 33 minutes, or until the cookie layer is golden at the edges and a toothpick inserted into the center comes out with a few moist crumbs. Avoid overbaking to maintain the fudgy texture.
06 - Allow the brookies to cool completely in the pan on a wire rack. Once fully set, use the parchment overhang to lift the slab out and cut into 16 squares.