Brownie Base

1. Place the 12 oz chocolate chips and the cubed butter in a large, microwave-safe bowl. Heat in 30-second bursts on high, stirring between each burst, until the chocolate and butter are fully melted and smooth.
2. Stir in the ¾ cup sugar and 1 teaspoon vanilla until evenly incorporated.
3. Add the eggs one at a time, mixing after each addition until the batter is uniform.
4. In a separate small bowl, whisk together the cocoa powder, cornstarch, and salt.
5. Add the dry ingredients to the chocolate mixture and stir vigorously for about 1–2 minutes, until the batter becomes smooth and starts to pull away from the sides of the bowl.
6. Fold in the 1 cup mini chocolate chips.
7. Spoon about two-thirds of the brownie batter into the prepared pan and spread into an even layer with a spatula. Reserve the remaining batter for the top.

Cheesecake Topping

1. In a mixer (stand or hand), beat the softened cream cheese until light and fluffy.
2. Add the ½ cup sugar and mix until combined.
3. Beat in the egg and ½ teaspoon vanilla until the filling is smooth and lump-free.
4. Dollop or spoon the cheesecake mixture over the brownie layer and gently spread into a thin, even layer with an offset spatula.

Finish & Bake

1. Drop spoonfuls of the remaining brownie batter over the cheesecake layer — use the back of the spoon to create small mounds or gentle swirls.
2. Bake in the preheated oven for 30–35 minutes, or until a toothpick inserted near the center comes out with just a few moist crumbs attached. Start checking at 30 minutes and judge doneness by the toothpick rather than the clock.
3. Remove from the oven and allow the pan to cool completely on a wire rack. Once cooled, use the parchment overhang to lift the slab from the pan and slice into squares.