Grease a 9-inch springform pan with cooking spray, then wrap it tightly with aluminum foil. Mix chocolate wafer crumbs and melted unsalted butter; press firmly into the bottom of the pan. Bake at 325°F for 10 minutes and cool completely.

Set up a double boiler and melt coarsely chopped bittersweet chocolate. Stir until smooth and glossy, then set aside to cool slightly.

Blend room-temperature cream cheese in a food processor until smooth. Gradually mix in granulated sugar, light brown sugar, and unsweetened cocoa powder. Add eggs, heavy cream, and melted chocolate; mix well. Stir in vanilla extract.

Pour the filling into the cooled crust, spread evenly. Place the pan in a larger baking dish with hot water. Bake at 325°F for about 1 hour and 10 minutes.

Cool the cheesecake completely on a wire rack. Cover and refrigerate for at least 6 hours or overnight.

Heat heavy cream for ganache until simmering; pour over chopped chocolate. Whisk until smooth, then stir in room-temperature butter.

Once the cheesecake has chilled, pour the ganache over the top, spreading it evenly. Let it sit at room temperature for about 1 hour before serving.