Prepare the Oven and Pan:
Preheat your oven to 350°F (175°C). Lightly spray a 9-inch square baking pan with cooking spray. Line the pan with parchment paper, leaving an overhang on the sides for easy removal. Set the pan aside.
Make the Brownies:
In a large microwave-safe bowl, combine the chocolate chips and butter. Melt in 30-second increments on high heat in the microwave, stirring in between each interval, until smooth and fully melted.
Stir in the sugar and vanilla extract until completely combined. Add the eggs one at a time, stirring well after each addition until fully incorporated.
In a small bowl, whisk together the cocoa powder, cornstarch, and salt. Add the dry mixture to the wet mixture, stirring vigorously until the batter is smooth and begins to pull away from the sides of the bowl. This should take about one to two minutes. Stir in the mini chocolate chips.
Pour two-thirds of the brownie batter into the prepared baking pan and smooth the top with a spatula. Set the remaining brownie batter aside.
Make the Cheesecake Layer:
Using a stand mixer or a handheld mixer, beat the softened cream cheese until light and fluffy. Add the sugar and beat until fully combined. Beat in the egg and vanilla extract until the mixture is smooth.
Spoon the cheesecake filling over the brownie batter in the pan, carefully spreading it into a thin, even layer using an offset spatula. Drizzle or spoon the remaining brownie batter over the top of the cheesecake layer.
Bake the Brownies:
Bake the brownies in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Keep a close eye on the brownies after 30 minutes to avoid overbaking.
Cool and Serve:
Let the brownies cool completely in the pan. Once cooled, use the parchment paper overhang to lift the brownies out of the pan. Cut into squares and serve. Store any leftovers in an airtight container in the refrigerator.