Preheat the oven to 350°F (175°C). Grease a 9×13 inch baking pan or line it with parchment paper.
In a large mixing bowl, combine the melted butter and granulated sugar. Mix well until smooth and creamy.
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the all-purpose flour, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the semi-sweet chocolate chips evenly throughout the batter.
Pour half of the batter into the prepared baking pan and spread it evenly.
In a small bowl, mix the brown sugar with 1/4 cup of the prepared batter to create a sugar cookie layer.
Drop spoonfuls of the sugar cookie mixture over the brownie batter in the pan, then gently spread it out to cover the surface.
Pour the remaining brownie batter over the sugar cookie layer and spread evenly.
Bake in the preheated oven for 22 to 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Remove from the oven and allow to cool completely in the pan on a wire rack.
Once cooled, dust the top with powdered sugar before slicing into 16 squares and serving.