Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan with butter or line it with parchment paper for easy removal.

In a mixing bowl, combine ½ cup melted unsalted butter with 1 cup of granulated sugar. Whisk until well blended.

Incorporate 2 large eggs and 1 teaspoon of vanilla extract into the mixture, stirring until the eggs are fully combined.

Add 1/3 cup cocoa powder, 1 cup all-purpose flour, ¼ teaspoon salt, and ¼ teaspoon baking powder. Use a spatula to stir gently until just combined. The batter should be thick and fudgy.

Spread the brownie batter evenly in the prepared baking pan. Use a spatula to smooth out the top for a nice finish.

In a separate bowl, cream together ½ cup softened butter, ½ cup granulated sugar, and ½ cup brown sugar until light and fluffy.

Add 1 large egg and 1 teaspoon of vanilla extract to the cookie mixture, blending until smooth.

Mix in 1 ¼ cups all-purpose flour, ½ teaspoon baking soda, and ¼ teaspoon salt. Fold in 1 cup of chocolate chips to create a soft and chewy cookie dough.

Dollop spoonfuls of the cookie dough over the brownie layer in the baking pan. Spread gently using your spatula or the back of a spoon to create an even layer.

Bake in the preheated oven for 25-30 minutes. The top should look golden brown, and a toothpick inserted into the center will come out with a few moist crumbs.

Once baked, remove from the oven and let cool in the pan for at least 15 minutes before slicing. This helps the brownies set and makes them easier to cut.