01 - Preheat oven to 350°F. Line an 8x8 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.
02 - In a medium bowl, whisk together melted butter and sugar until well combined. Add eggs and vanilla extract, whisking until smooth and glossy. Fold in flour, cocoa powder, and salt until just incorporated. Spread the batter evenly across the bottom of the prepared baking pan.
03 - Beat softened butter, brown sugar, and granulated sugar together until light and creamy. Mix in the egg and vanilla extract until fully blended. In a separate bowl, whisk together 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 cookie dough evenly over the brownie batter. Gently spread with a spatula to cover the surface — it is fine if some brownie batter peeks through.
05 - Bake for 28 to 33 minutes, or until the cookie layer turns golden and a toothpick inserted into the center comes out with a few moist crumbs. Avoid overbaking to maintain a fudgy texture.
06 - Let the brookies cool completely in the pan. Use the parchment overhang to lift the slab out, then cut into 16 even bars.