Preheat your oven to 350°F (175°C). Crush about 20 Oreo cookies into fine crumbs and mix with 2 tablespoons of melted butter and 2 tablespoons of sugar until combined. Press into the bottom of an 8-inch springform pan to form a crust. Bake for 12-14 minutes and cool completely.

Lower oven temperature to 300°F (150°C). Place a baking tray filled with water on the bottom rack to create steam.

Melt ¾ cup of chocolate chips in a heatproof bowl in the microwave in 20-second intervals, stirring until smooth. Set aside to cool.

Beat together cream cheese, granulated sugar, and cornstarch until smooth. Add eggs one at a time, then sour cream and vanilla extract, mixing gently.

Scoop out 1 ½ cups of this filling into another bowl and fold in the melted chocolate until fully integrated.

Pour dollops of vanilla cheesecake batter over the crust, followed by spoonfuls of the chocolate batter. Swirl together with a knife or skewer.

Bake for 15 minutes at 300°F (150°C). Then reduce to 225°F (110°C) and bake for an additional 2 hours without opening the door.

Turn off the oven and let the cheesecake sit for 1 hour with the door closed. Crack the door and cool for another hour.

Refrigerate covered for 3-4 hours or overnight for best flavor and texture.

Top with whipped cream and chocolate shavings before serving. Use a warm knife to slice.