Set your oven to 350°F (175°C). Line an 8×8-inch pan with parchment paper or lightly grease it with nonstick spray.
Melt chocolate chips and butter in a microwave-safe bowl in 30-second intervals, stirring each time, until smooth. Let it cool slightly.
Whisk in sugar and vanilla. Add eggs one at a time, whisking until glossy. Sift in cocoa powder, cornstarch, and salt. Whisk until smooth.
Fold in mini chocolate chips. Spread the batter evenly in the prepared pan.
In a separate bowl, beat softened cream cheese until smooth. Add sugar, egg, and vanilla. Beat until creamy and fluffy.
Drop spoonfuls of the cheesecake batter over the brownie layer. Swirl gently with a knife or skewer to create a marbled look—don’t overmix.
Bake for 30–35 minutes until edges are set and the center is slightly jiggly. A toothpick should come out with moist crumbs, not wet batter.
Let cool completely in the pan on a wire rack. Then refrigerate for 1–2 hours to fully set the cheesecake layer before slicing.