Preheat your oven to 350°F (175°C). Prepare the crust by combining crushed Oreo cookies with melted unsalted butter until well blended. Press this mixture into the bottom of a 9-inch springform pan.

In a mixing bowl, beat together cream cheese and granulated sugar until smooth and creamy. Add eggs, red velvet cake mix, and vanilla extract, mixing until fully combined.

In a separate bowl, beat another block of cream cheese with sugar and vanilla extract until creamy. This will be the vanilla layer.

Pour the red velvet cheesecake mixture over the prepared Oreo crust, then dollop the vanilla cheesecake mixture on top and gently swirl to create a marbled effect.

Bake in the preheated oven for 45-50 minutes until set around the edges but slightly jiggly in the center.

Turn off the oven, leaving the cheesecake inside for 1 hour to cool gently.

Transfer the cheesecake to the fridge and let it chill for at least 6 hours or overnight for optimal texture.

For the ganache, heat heavy cream in a saucepan until simmering, then pour over chopped dark chocolate and stir until smooth.

Allow the ganache to cool slightly before drizzling it over the chilled cheesecake. Decorate with whipped cream or crushed Oreo crumbs before serving.