Preheat your oven to 325°F (163°C). Grease a 9-inch springform pan and wrap it in aluminum foil. Combine chocolate wafer crumbs with melted butter and press into the pan. Bake for 10 minutes, then cool completely.

Set up a double boiler and melt bittersweet chocolate until smooth. Allow to cool slightly.

In a food processor, blend cream cheese until smooth. Gradually add granulated sugar, light brown sugar, and cocoa powder, mixing until incorporated. Add eggs and heavy cream, blending until smooth. Fold in melted chocolate and vanilla extract.

Pour the filling over the cooled crust. Place the pan in a larger roasting pan filled with hot water halfway up the sides. Bake for about 1 hour and 10 minutes, until edges are set and the center jiggles slightly.

Cool the cheesecake to room temperature, then cover and refrigerate for at least 6 hours.

For the ganache, heat heavy cream until simmering. Pour over chopped chocolate and whisk until smooth. Stir in unsalted butter until melted.

Pour ganache over chilled cheesecake and let set at room temperature for an hour before slicing and serving.