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

In a large bowl, combine chocolate chips and butter. Microwave in 30-second intervals, stirring between each, until smooth.

Stir in sugar and vanilla until combined. Add eggs one at a time, stirring after each addition.

In a separate small bowl, whisk together cocoa powder, cornstarch, and salt. Add to the wet ingredients and stir vigorously for 1–2 minutes until smooth and the batter pulls away from the sides. Stir in mini chocolate chips.

Pour 2/3 of the brownie batter into the prepared pan and smooth the top.

Using a hand or stand mixer, beat the cream cheese until light and fluffy. Add sugar and beat until combined, then mix in 1 egg and vanilla until smooth.

Spoon the cheesecake filling evenly over the brownie base, then drizzle or spoon the remaining brownie batter over the top.

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

Let cool completely in the pan. Use the parchment overhang to lift out the brownies and cut into squares.