Preheat your oven to 350°F (175°C).
Line your baking pan with parchment paper, creating a sling with overhanging edges on two sides, and lightly grease any exposed areas.
In a large microwave-safe bowl, combine the chopped chocolate and butter. Microwave in 30-second intervals, stirring between each, until completely melted and smooth.
8 oz High-quality semi-sweet chocolate, 1/2 cup Unsalted butter
Whisk in the granulated sugar and brown sugar until fully incorporated. The mixture should look glossy and smooth.
1 cup Granulated sugar, 1/4 cup Light brown sugar
Beat in the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.
3 Large eggs, 1 teaspoon Vanilla extract
Fold in the flour, cocoa powder, and salt until just combined and no dry streaks remain.
3/4 cup All-purpose flour, 1/4 cup Unsweetened cocoa powder, 1/2 teaspoon Salt
If using, fold in chocolate chips to enhance the chocolate flavor of the brownies.
1/2 cup Chocolate chips
Pour about ⅔ of the brownie batter into the prepared pan and spread it evenly. Set aside the remaining brownie batter for the swirl topping.
In a separate bowl, beat the room temperature cream cheese with an electric mixer until completely smooth and free of lumps, about 2 minutes.
8 oz Full-fat block-style cream cheese
Beat in the sugar and pinch of salt until the mixture is smooth and creamy.
1/4 cup Granulated sugar, 1 pinch Salt
Beat in the room temperature egg and vanilla extract until just combined. Be careful not to overmix.
1 Large egg, 1/2 teaspoon Vanilla extract
Pour the cheesecake mixture on top of the brownie batter layer in the prepared pan, spreading it evenly with a spatula.
Dollop spoonfuls of the reserved brownie batter over the cheesecake layer. Make sure to distribute these dollops evenly across the surface.
Use a knife or skewer to gently swirl the layers together, creating a marbled effect. Draw the knife through the batters in long, sweeping motions. Don't over-swirl.
Bake at 350°F (175°C) for 35-40 minutes. The edges should be set while the center remains slightly jiggly.
Check for doneness by inserting a toothpick into the center—it should come out with a few moist crumbs attached, but not wet batter.
Let the brownies cool gradually in the pan placed on a wire rack for at least 1 hour at room temperature.
Once mostly cool, transfer the pan to the refrigerator to chill thoroughly for at least 3-4 hours or preferably overnight before cutting.
For clean cuts, run a sharp knife under hot water, wipe it dry, then make your cut. Repeat between each slice.