Preheat the oven to 325°F (165°C). Lightly grease a 9-inch springform pan.
Combine graham cracker crumbs and melted butter. Press firmly into the base of the pan to form the crust.
Pour melted dark chocolate over the crust and spread evenly. Chill for 10 minutes to set.
Beat cream cheese and sugar until smooth. Add eggs one at a time, then blend in vanilla, sour cream, and heavy cream. Mix until creamy but not overbeaten.
Pour the batter over the crust. Place the pan in a larger baking dish and fill halfway with hot water for a bain-marie. Bake for 55–65 minutes, until the center is slightly wobbly.
Turn off the oven, crack the door open, and let the cheesecake rest inside for 1 hour to cool gradually.
Heat heavy cream in a saucepan until it begins to simmer. Pour over chocolate chips, let sit for 1–2 minutes, then stir until smooth and glossy.
Once the cheesecake is fully cooled, pour ganache over the top and spread evenly.
Refrigerate for at least 4 hours or overnight before slicing and serving.
