01 - Preheat oven to 350°F. Line a 9x9 inch square baking pan with parchment paper, leaving a slight overhang on two sides for easy removal.
02 - In a medium bowl, whisk melted butter and granulated sugar until well combined. Add eggs and vanilla extract, beating until the mixture becomes glossy and smooth. Fold in cocoa powder, flour, and salt until just incorporated — do not overmix. Spread the batter evenly across the bottom of the prepared pan.
03 - In a separate bowl, cream softened butter with brown sugar and granulated sugar until light and fluffy, about 2 minutes. Beat in the egg and vanilla extract until fully blended. Add flour, baking soda, and salt, mixing until just combined. Gently fold in the chocolate chips.
04 - Drop spoonfuls of cookie dough evenly over the brownie batter. Gently flatten and spread the cookie dough using an offset spatula or the back of a spoon to mostly cover the brownie layer. A little brownie peeking through is perfectly fine and adds to the rustic look.
05 - Bake for 30 to 35 minutes until the edges are golden brown and the center is just set. Avoid overbaking — the brookies should remain fudgy and slightly soft in the middle.
06 - Allow the brookies to cool completely in the pan before using the parchment overhang to lift them out. Cut into 16 even squares with a sharp knife.