Step 1: Preheat your oven to 350°F (175°C) and grease a 9x9 inch baking pan or line it with parchment paper.
Step 2: In a medium bowl, whisk together the melted butter and 1 cup of sugar for the brownie layer. Add 2 eggs and 1 tsp vanilla, beating until smooth.
Step 3: Sift in the cocoa powder, 1/2 cup flour, and 1/4 tsp salt. Fold gently until just combined. Spread the brownie batter evenly into the bottom of the prepared pan.
Step 4: 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 5: Beat in the egg and vanilla extract for the cookie dough. In a small bowl, whisk 1 1/4 cups flour, baking soda, and 1/2 tsp salt, then gradually add to the wet ingredients.
Step 6: Stir in the chocolate chips by hand. Drop rounded tablespoons of the cookie dough over the top of the brownie batter.
Step 7: Bake for 25-30 minutes, or until the cookie top is golden brown and a toothpick inserted into the center comes out with just a few moist crumbs.
Step 8: Allow the bars to cool completely in the pan before slicing into 16 squares.