Preheat oven to 350°F (175°C). Lightly grease a 9-inch square baking pan and line with parchment, leaving overhang for easy removal.

In a large bowl, melt the chocolate chips and butter together in the microwave using 30-second bursts, stirring between each until smooth.

Mix in sugar and vanilla until fully blended. Add eggs one at a time, stirring after each addition until batter is thick and glossy.

In a separate bowl, combine cocoa powder, cornstarch, and salt. Add dry ingredients to the wet mixture and stir vigorously until the batter pulls away from the sides of the bowl.

Fold in the mini chocolate chips. Pour about two-thirds of the brownie batter into the prepared pan and smooth it into an even layer.

In another bowl, beat softened cream cheese until fluffy. Add sugar and beat until combined. Mix in egg and vanilla until smooth and creamy.

Spread the cheesecake mixture gently over the brownie layer using an offset spatula.

Spoon the remaining brownie batter over the top and lightly swirl or spread for a marbled effect.

Bake for 30 to 35 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs.

Let the brownies cool completely in the pan, then refrigerate until set before slicing and serving.