Preheat your oven to 325°F (163°C). Prepare a 9-inch springform pan by greasing it and lining the bottom with parchment paper.

In a small bowl, combine the chocolate graham cracker crumbs, granulated sugar, and melted butter. Stir well until the mixture resembles wet sand. Press this mixture into the bottom of the prepared pan firmly to form the crust. Bake for 10 minutes, then remove from the oven and allow it to cool.

In a large mixing bowl, beat the softened cream cheese and sugar together until smooth and creamy. Add the eggs one at a time, ensuring you beat well after each addition. Mix in the vanilla extract. Carefully fold in the melted semi-sweet chocolate and sour cream until the mixture is well-combined. Pour this silky filling over the cooled crust.

In a separate bowl, beat the softened cream cheese with powdered sugar until smooth. Add the melted white chocolate and sour cream, mixing until well combined. Gently pour this mixture over the chocolate cheesecake layer, spreading it evenly.

Place the springform pan in the oven and bake for 45-50 minutes, or until the center is just set (it may still jiggle slightly). Turn off the oven but leave the cheesecake inside for an additional hour to cool gradually, avoiding cracks.

After cooling to room temperature, place the cheesecake in the refrigerator for at least 4 hours, or preferably overnight, to chill and firm up.

In a small saucepan, heat the heavy cream until it begins to simmer. Pour the hot cream over the chopped dark chocolate in a heatproof bowl. Stir until the mixture becomes smooth and glossy.

Pour the dark chocolate ganache over the chilled cheesecake and spread it evenly with a spatula. Refrigerate again for 1-2 hours to allow the ganache to set.

Once the ganache is firm, remove the cheesecake from the springform pan, transfer it to a serving platter, slice, and savor each chocolatey bite!