Preheat your oven to 325°F (160°C) and prepare a 9x9 inch baking pan with nonstick spray and parchment paper.

In a mixing bowl, beat the cream cheese until smooth, then add sugar, vanilla extract, and eggs, mixing until combined. Fold in Oreo cookies.

In a separate bowl, sift together flour, cocoa powder, cornstarch, and salt.

Beat together eggs, sugar, and an egg yolk until fluffy. Gradually add melted butter, oil, and vanilla extract. Combine with dry ingredients.

Fold in chocolate chips and spread three-quarters of the brownie batter into the prepared pan.

Pour the cheesecake mixture over the brownie layer and swirl spoonfuls of the remaining brownie batter on top.

Bake for 45-55 minutes, ensuring edges are firm and the center has a slight jiggle.

Allow brownies to cool in the oven with the door slightly ajar for 15 minutes, then transfer to a wire rack.

Chill in the refrigerator for at least 6 hours before serving.