01 - Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving enough overhang on the sides to lift the finished brookies out easily.
02 - In a large bowl, whisk the melted butter with granulated sugar and brown sugar until well combined. Add the eggs and vanilla extract, whisking vigorously until the mixture is glossy and smooth. Sift in the flour, cocoa powder, and salt, then fold gently just until no dry streaks remain. Fold in the chocolate chips.
03 - Pour the brownie batter into the prepared pan and spread it into an even layer across the bottom.
04 - In a medium bowl, beat the softened butter with brown sugar and granulated sugar using a hand mixer until light and fluffy, about 2 minutes. Add the egg and vanilla, beating until fully incorporated.
05 - In a separate small bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the butter mixture, stirring until just combined. Fold in the chocolate chips.
06 - Drop spoonfuls of the cookie dough evenly over the brownie batter. Gently spread and swirl the cookie dough with a spatula to partially cover the brownie layer, leaving some gaps for the brownie to peek through.
07 - Bake for 28 to 32 minutes, or until the top is lightly golden and a toothpick inserted into the center comes out with moist fudgy crumbs attached but not wet batter.
08 - Allow the brookies to cool completely in the pan on a wire rack. Once fully cooled, use the parchment overhang to lift them out and cut into 16 squares.