Melt the chocolate

• Fill a saucepan with a small amount of water and bring it to a boil.
• Place a plate slightly larger than the saucepan with the chopped dark chocolate on top, making sure it doesn't touch the water.
• Stir the chocolate until smooth, then let it cool to room temperature.
• Melt the white chocolate using the same method.

Make the Oreo crust

• Place the Oreos in a food processor and pulse until fine crumbs form.
• Melt the unsalted butter in a saucepan over low heat.
• Place the Oreo crumbs in a deep bowl, add the melted butter and mix until combined.
• Press the cookie dough onto the bottom of a baking pan using the back of a spoon.

Make the dark chocolate batter

• Place part of the cream cheese in a deep bowl at room temperature.
• Add the melted dark chocolate and mix well.
• Add the granulated sugar, vanilla sugar and remaining cream cheese and mix until well combined.
• Add the cornstarch and mix again, then switch to a spatula.
• Add the eggs one at a time, mixing lightly after each addition without overmixing.

Make the white chocolate batter

• Place part of the cream cheese in a deep bowl at room temperature.
• Add the melted white chocolate and mix well.
• Add the granulated sugar, vanilla sugar and remaining cream cheese and mix until well combined.
• Add the cornstarch and mix again, then switch to a spatula.
• Add the eggs one at a time, mixing lightly after each addition without overmixing.

Assemble and bake

• Pour the dark chocolate cheesecake batter onto the Oreo crust.
• Pipe the white cheesecake batter on top.
• Preheat the oven to 125 °C.
• Bake until the sides are firm and the center jiggles slightly.
• Turn off the oven and let the cheesecake cool in the oven.

Make the ganache topping

• Heat the heavy cream until it's about to boil.
• Add the chopped dark chocolate and let it sit.
• Mix until smooth.
• Pour the chocolate ganache over the cheesecake and spread it evenly.

Chill and serve

• Cover the cheesecake and refrigerate until firm, preferably overnight.