Prepare the Brownie Layer

1. Preheat your oven to 350°F (175°C). Grease an 8×8-inch baking pan or line it with parchment paper for easy removal.
2. Mix the wet ingredients by whisking together the melted butter and sugar in a large bowl. Stir until smooth.
3. Add the eggs and vanilla extract and whisk until fully combined and slightly glossy.
4. Sift in the dry ingredients by adding the cocoa powder, flour, salt, and baking powder. Stir until just combined.
5. Pour the brownie batter into the prepared pan and spread it evenly with a spatula.

Prepare the Cookie Layer

1. Cream the butter and sugars in a separate bowl until light and fluffy.
2. Add the egg and vanilla extract and beat until well combined.
3. Mix the dry ingredients in a separate bowl, then gradually add them to the wet ingredients, mixing until just incorporated.
4. Fold in the chocolate chips using a spatula to evenly distribute them.
5. Drop spoonfuls of the cookie dough over the brownie layer, gently spreading it out but not fully covering the brownie batter.

Bake and Cool

1. Bake for 30-35 minutes or until the cookie layer is golden and a toothpick inserted into the center comes out with a few moist crumbs.
2. Cool the brookies in the pan for at least 15 minutes before slicing into squares.