Prepare the Oreo Crust:

1. Preheat the oven to 350°F (175°C). Grease or line a 9-inch springform pan with parchment paper.
2. Pulse Oreo cookies in a food processor until finely crushed. Mix with melted butter until it resembles wet sand.
3. Press the mixture into the bottom of the prepared pan to form an even crust.
4. Bake for 8-10 minutes and let cool while preparing the cheesecake filling.

Prepare the Chocolate Cheesecake Filling:

1. Beat softened cream cheese, sugar, and vanilla until smooth.
2. Add eggs one at a time, mixing well after each addition.
3. Gradually add melted chocolate and continue mixing.
4. Stir in heavy cream and sour cream until smooth.
5. Pour the filling over the cooled Oreo crust and smooth the top.

Bake the Cheesecake:

1. Reduce the oven temperature to 325°F (163°C).
2. Bake the cheesecake for 55-65 minutes or until the edges are set and the center slightly jiggles.
3. Turn off the oven and cool the cheesecake inside with the door slightly ajar for 1 hour.
4. Let it cool completely at room temperature, then refrigerate for at least 4 hours or overnight.

Make the Chocolate Ganache:

1. Heat the heavy cream in a small saucepan until it simmers.
2. Remove from heat, add chopped chocolate, and stir until smooth.
3. Allow ganache to cool slightly before pouring it over the chilled cheesecake.

Assemble and Garnish:

1. Once the ganache has set, remove the cheesecake from the pan.
2. Pour ganache over the cheesecake and spread evenly.
3. Garnish with crushed Oreos and whole Oreos, if desired.