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 the melted butter and granulated sugar until well combined. Add the eggs and vanilla extract, whisking until the mixture is smooth and glossy.
03 - Gently fold in the flour, cocoa powder, and salt until just combined. Do not overmix. Spread the brownie batter evenly across the bottom of the prepared baking pan.
04 - In a separate bowl, beat the softened butter, brown sugar, and granulated sugar together until light and creamy. Mix in the egg and vanilla extract until fully incorporated.
05 - 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.
06 - Drop spoonfuls of the 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.
07 - Bake for 28 to 33 minutes, or until the cookie top is golden and a toothpick inserted into the center comes out with a few moist crumbs. Avoid overbaking to maintain a fudgy texture.
08 - Allow the brookies to cool completely in the pan. Use the parchment overhang to lift the slab out, then cut into 16 even bars.