Step 1: Preheat your oven to 350°F (175°C) and line an 8x8 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.
Step 2: In a medium bowl, whisk together the melted butter and 1 cup of granulated sugar for the brownie layer until well combined.
Step 3: Add two eggs and 1 tsp vanilla extract to the butter mixture, whisking vigorously until the batter is smooth and shiny.
Step 4: Sift in 1/2 cup flour, cocoa powder, and 1/4 tsp salt. Gently fold the dry ingredients into the wet until just combined, then spread evenly into the prepared pan.
Step 5: In a separate large bowl, cream together the softened butter, brown sugar, and 1/4 cup granulated sugar for the cookie layer until light and fluffy.
Step 6: Beat in one egg and 1 tsp vanilla extract. In a small bowl, whisk 1 1/4 cups flour, baking soda, and 1/4 tsp salt, then stir this into the cookie batter.
Step 7: Fold in the chocolate chips. Take rounded tablespoons of the cookie dough and flatten them slightly with your hands before placing them on top of the brownie batter.
Step 8: Bake for 30-35 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs. Do not overbake!
Step 9: Allow the brookies to cool completely in the pan before lifting them out using the parchment paper and slicing into 16 squares.