Preheat oven to 350°F (175°C). Grease or line a 9×13-inch baking dish with parchment paper.
Whisk melted butter, sugar, eggs, and vanilla until glossy.Sift in cocoa powder, flour, salt, and baking powder. Stir until just combined.Spread batter evenly in the prepared pan.
Cream softened butter with granulated and brown sugar until light and fluffy.Beat in egg and vanilla.
In a separate bowl, whisk flour, baking soda, and salt. Gradually mix into wet ingredients.
Fold in chocolate chips.
Drop spoonfuls of cookie dough over brownie batter. Gently spread to cover the surface.
Bake 25–30 minutes, until golden on top and a toothpick comes out with moist crumbs.
Cool completely before slicing into squares.
