Preheat oven to 350°F (175°C). Line a 9×9-inch pan with parchment paper, leaving overhang 'handles,' and lightly spray with non-stick cooking spray.

In a bowl, whisk together melted butter and granulated sugar until smooth. Add eggs, one at a time, and stir in vanilla extract. In another bowl, sift together cocoa powder, flour, and salt; gently fold this into the wet mixture until just combined. Fold in chocolate chips.

Cream together softened butter, granulated sugar, and brown sugar using a mixer for 2–3 minutes, until pale and fluffy. Beat in egg and vanilla extract. Whisk together flour, baking soda, and salt separately, then add to the butter mixture on low speed until combined. Fold in chocolate chips by hand.

Spread the brownie batter evenly in the prepared pan. Top with cookie dough, flattening small pieces between your palms or dropping spoonfuls across the surface and gently smoothing to cover.

Bake for 30–35 minutes, until the top is golden and a toothpick inserted in the center comes out with a few moist crumbs. Let the brookies cool in the pan for at least 30 minutes. Lift out using the parchment handles, place on a board, and slice into 16 squares.