Preheat the oven to 325°F (160°C) and grease a 9-inch springform pan.

Combine the chocolate cookie crumbs, granulated sugar, and melted butter in a medium bowl. Mix until well incorporated.

Press the mixture firmly into the bottom of the prepared springform pan. Bake for 10 minutes, then let cool.

Beat the softened cream cheese in a large mixing bowl until smooth and creamy.

Gradually add the granulated sugar, mixing until fully combined. Add the eggs one at a time, ensuring each is mixed well. Stir in the vanilla extract.

Blend in the melted chocolate and cocoa powder until smooth. Mix in the sour cream until combined.

Pour the cheesecake filling over the cooled crust, spreading it evenly.

Bake for 60–70 minutes, or until the center is set but slightly jiggly. Turn off the oven, leaving the cheesecake inside for 1 hour.

Remove from the oven and let cool at room temperature for about 30 minutes. Refrigerate for at least 4 hours.

Heat the heavy cream in a small saucepan until simmering. Remove from heat, add the chopped chocolate, and let sit for 1 minute. Stir until smooth.

Pour the chocolate ganache over the chilled cheesecake, spreading it evenly.

Carefully remove the sides of the springform pan, slice, and serve chilled.