01 - Preheat your oven to 350°F. Line an 8x8 inch baking pan with parchment paper, allowing enough overhang on the sides to lift the brownies out easily after baking.
02 - In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until completely smooth. Add the eggs and vanilla extract, beating until fully incorporated.
03 - Sift the flour, cocoa powder, and salt directly into the wet mixture. Stir gently until just combined — be careful not to overmix. Fold in the chopped dark chocolate.
04 - Set aside approximately 1/4 cup of the brownie batter for the swirl topping. Pour the remaining batter into your prepared pan, using a spatula to spread it evenly.
05 - In a separate bowl, beat the softened cream cheese until completely smooth and creamy. Add the granulated sugar, egg, and vanilla extract, mixing until no lumps remain.
06 - Spread the cheesecake mixture evenly over the brownie batter in the pan, creating a distinct white layer on top.
07 - Drop spoonfuls of the reserved brownie batter randomly over the cheesecake layer. Run a knife or skewer through both layers in a swirling motion to create a marbled pattern — don't over-swirl or you'll lose the distinction.
08 - Bake for 32 to 35 minutes. The center should be just set, and a toothpick inserted should come out with a few moist crumbs — not completely clean, or they'll be overdone.
09 - Let the brownies cool completely in the pan. Once at room temperature, use the parchment overhang to lift them out, then cut into 16 even squares.