1. Prepare the Chocolate:

1. Melt the dark chocolate (150g) using a double boiler method. Let it cool to room temperature.
2. Melt the white chocolate using the same method.

2. Prepare the Cookie Dough:

1. Place the Oreos in a food processor and pulse until fine crumbs form.
2. Melt the unsalted butter in a saucepan over low heat.
3. Mix the Oreo crumbs with the melted butter until well combined.
4. Press the mixture onto the bottom of a baking pan using the back of a spoon.

3. Prepare the Dark Chocolate Batter:

1. In a deep bowl, combine 200g of cream cheese (at room temperature) with the melted dark chocolate. Mix well.
2. Add granulated sugar, vanilla sugar, and remaining cream cheese. Mix until well combined.
3. Add cornstarch and mix again. Use a spatula instead of a mixer from now on.
4. Add eggs one at a time, mixing lightly after each addition (do not overmix).

4. Prepare the White Chocolate Batter:

1. In a deep bowl, combine 200g of cream cheese (at room temperature) with the melted white chocolate. Mix well.
2. Add granulated sugar, vanilla sugar, and remaining cream cheese. Mix until well combined.
3. Add cornstarch and mix again. Use a spatula instead of a mixer from now on.
4. Add eggs one at a time, mixing lightly after each addition (do not overmix).

5. Assemble and Bake:

1. Pour the dark chocolate batter onto the Oreo crust.
2. Pipe the white chocolate batter on top using a piping bag for an even layer.
3. Preheat the oven to 125°C. Bake the cheesecake for 75-80 minutes, or until the sides are firm and the center jiggles slightly.
4. Turn off the oven and let the cheesecake cool in the oven for 1 hour to prevent cracking or sinking.

6. Prepare the Topping:

1. Heat the heavy cream until it’s about to boil. Add the chopped dark chocolate (75g) and let it sit for 1 minute. Mix until smooth.
2. Pour the chocolate ganache over the cheesecake and spread it evenly.
3. Cover the cheesecake and refrigerate until firm, preferably overnight.
4. Once firm, slice the cheesecake and garnish with chopped hazelnuts, sliced strawberries, and optionally a half of Ferrero Rocher or any other desired decoration.