Preheat the oven to350F. Line an 8x8 square pan with two sheets of parchment paper, making sure the parchment extends over the sides of the pan to form a "sling". Secure the sides with binder clips if you would like.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the cream cheese and sugar until smooth and creamy, stopping to scrape the bowl often.
1 cup cream cheese, room temperature, ¼ cup granulated sugar
Beat in the egg, cornstarch and vanilla until thoroughly combined.
1 teaspoon cornstarch, 1 large egg, room temperature, ½ teaspoon pure vanilla extract
In medium bowl, whisk together the flour, cocoa powder and salt. Whisk to break up any lumps in the cocoa powder.
¾ cup all purpose flour, 1 tablespoon cocoa powder, ½ teaspoon fine sea salt
In a medium saucepan over low heat, melt the butter and espresso powder. Remove from the heat.
½ cup unsalted butter, 1 teaspoon espresso powder
Stir in the chocolate chips until fully melted and smooth. If there is chocolate that hasn’t melted, put back on low heat and stir until melted.
¾ cup chocolate chips, bittersweet or semi-sweet
Whisk in the granulated sugar and brown sugar.
¾ cup granulated sugar, ¼ cup light brown sugar, packed
Whisk in the eggs, one at a time, and the vanilla
3 large eggs, room temperature, 1 teaspoon pure vanilla extract
Fold in the flour mixture, stirring until just combined. Scrape down the sides and bottom of the bowl to ensure everything is fully mixed.
Fold in half of the chopped Oreos.
1 cup chopped Oreos, divided
Reserve ¼ cup of brownie batter. Spread the remaining brownie batter into prepared pan in an even layer.
Pour the cheesecake batter on top of the brownie batter and smooth with an offset spatula.
Dollop spoonfuls of the reserved brownie batter over the cheesecake batter. Create swirls with the batters with a toothpick.
Sprinkle the remaining Oreos on top of the brownies.
Bake for 28-35 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs, and the edges are starting to turn a light golden.
Cool the brownies to room temperature, then place in the refrigerator to chill for at least an hour. Serve chilled or room temperature.