1-Melt the 12 tablespoons of unsalted butter and ½ cup semisweet chocolate chips together in the microwave, using 30-second intervals while stirring until smooth, then mix in the ½ cup unsweetened cocoa powder.

2-Add 1 cup granulated sugar and ½ cup packed brown sugar, stirring well to combine.

3-Beat in the 2 large eggs and 1 large egg yolk one at a time, making sure each is fully incorporated before adding the next.

4-Stir in 1 teaspoon vanilla extract and ½ teaspoon salt to enhance the flavors.

5-Add 1 cup flour and mix until the batter is smooth; reserve ¼ cup of this batter for later.

6-Spread the remaining batter evenly in the prepared pan.

7-For the cheesecake swirl, beat 8 ounces of softened cream cheese with ¼ cup granulated sugar until creamy, then add 1 large egg and ½ teaspoon vanilla extract, beating until smooth.

8-Pour the cheesecake mixture over the brownie batter in the pan.

9-Drop the reserved brownie batter over the cheesecake layer and use a knife to swirl it gently for that marbled effect.

10-Bake for 25-30 minutes, until the center is set and a toothpick comes out with fudgy crumbs.

11-Let the brownies cool completely before cutting them into squares.