Preheat oven to 350°F (175°C). Grease an 8×8-inch baking pan. A well-greased or parchment-lined pan ensures clean edges and easy release once the brownies cool.
Mix the melted butter, granulated sugar, and eggs until smooth. The mixture should become glossy and slightly thick, which helps create a fudgy brownie texture. Add the cocoa powder, flour, salt, and baking powder, stirring just until combined to avoid overmixing and toughening the batter.
In a separate bowl, beat the softened cream cheese, powdered sugar, and vanilla until creamy and lump-free. A smooth mixture ensures clean, defined swirls in the finished brownies.
Pour the brownie batter into the prepared pan, spreading it evenly into the corners. Drop spoonfuls of the cream cheese mixture across the surface, spacing them so the swirl pattern distributes evenly.
Use a knife to swirl the cream cheese into the brownie batter with gentle figure-eight motions. Avoid over-swirling—defined ribbons of cream cheese bake into beautiful marbled patterns. Bake for 25–30 minutes, or until the center is set and a toothpick comes out with moist crumbs.
