• Preheat the oven to 350°F (175°C). Line a 9x9 inch baking pan with parchment paper.

Make Brownie Batter

• Melt the butter for the brownie layer in a microwave-safe bowl. Let it cool slightly.
• In a large bowl, stir together the melted butter, granulated sugar, eggs, and vanilla until well combined. Add the cocoa powder, flour, salt, and baking powder and stir until smooth.
• Spread the brownie batter evenly into the prepared pan and smooth the top with a spatula. Set aside.

Make Cookie Dough

• In a separate bowl, cream together the room temperature butter, granulated sugar, and brown sugar until light and fluffy. Add the egg and vanilla and mix until combined.
• In another bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients and mix until just combined. Fold in the chocolate chips.

Assemble and Bake

• Drop spoonfuls of cookie dough over the brownie batter. Use a spatula or your fingers to gently press the cookie dough down into the brownie layer.
• Bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Both layers should look set.
• Cool completely in the pan on a wire rack. Lift out using the parchment paper and cut into squares.