Prepare the Brownie Base

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a 9×9-inch baking pan or line it with parchment paper for easy removal.
2. Mix the Wet Ingredients: In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
3. Combine the Dry Ingredients: In a separate bowl, sift together the cocoa powder, flour, salt, and baking powder. Gradually add the dry ingredients to the wet ingredients, stirring until well combined. Add the milk and mix until the batter is smooth.
4. Pour the Batter into the Pan: Spread the brownie batter evenly into the prepared pan, smoothing the top with a spatula.

Prepare the Cream Cheese Swirl

1. Mix the Cream Cheese Filling: In a medium bowl, beat the softened cream cheese, granulated sugar, and vanilla extract until smooth and creamy. Add the egg and beat until fully combined.
2. Swirl the Cream Cheese: Drop spoonfuls of the cream cheese mixture over the brownie batter. Using a butter knife or skewer, swirl the cream cheese into the brownie batter, creating a marbled effect.

Bake the Brownies

1. Bake: Place the pan in the preheated oven and bake for 40-45 minutes, or until a toothpick inserted into the center of the brownies comes out with just a few moist crumbs.
2. Cool: Remove the brownies from the oven and allow them to cool in the pan for 15 minutes. Once they’ve cooled slightly, cut into squares and transfer them to a wire rack to cool completely.