1. Preheat oven to 325°F (163°C). Line a 9-inch (23cm) springform pan with parchment paper in the bottom and grease the sides.
2. Combine the crust ingredients in a small bowl. Press the mixture into the bottom and up the sides of the springform pan.
3. Bake the crust for 10 minutes, then set aside to cool.
4. Cover the outsides of the pan with aluminum foil so that water from the water bath cannot get in (see how I prepare my pan for a water bath). Set prepared pan aside.

CHEESECAKE

1. Reduce oven temperature to 300°F (148°C).
2. In a large bowl, beat the cream cheese, sugar and cocoa on low speed until well completely combined and smooth. Be sure to use low speed to reduce the amount of air added to the batter, which can cause cracks. Scrape down the sides of the bowl.
3. Add the sour cream and vanilla extract and mix on low speed until well combined.
4. Add the melted chocolate in three parts, stirring until combined after each. Adding it in parts helps ensure that it incorporates evenly and helps prevent clumping.
5. Add the eggs one at a time, mixing slowly to combine after each addition. Scrape down the sides of the bowl as needed to make sure everything is well combined.
6. Pour the cheesecake batter evenly into the crust.
7. Place the springform pan inside another larger pan. Fill the outside pan with enough warm water to go about halfway up the sides of the springform pan. The water should not go above the top edge of the aluminum foil on the springform pan.
8. Bake for 1 hour 5-10 minutes. The center should be set, but still jiggly.
9. Turn off the oven and leave the door closed for 30 minutes. The cheesecake will continue to cook, but slowly begin to cool as well.
10. Crack the door of the oven for 30 minutes to allow the cheesecake to continue to cool slowly. This process helps prevent cracking.
11. Remove the cheesecake from the oven and water bath wrapping and refrigerate until firm, 5-6 hours or overnight.
12. A couple hours before you’re ready to add the cheesecake topping, make the chocolate ganache for the swirls. Put the chocolate chips in a heat proof bowl.
13. Microwave the heavy whipping cream until it just begins to boil, then pour it over the chocolate chips. Allow it to sit for 2-3 minutes, then whisk until smooth.
14. Allow the ganache to sit and cool to room temperature, which should be the right consistency for piping. You can refrigerate it until it’s cold and firm, but then you will need to heat it for about 10-15 seconds in the microwave and stir it so that it’s soft enough to pipe, but still stiff enough to hold its shape.
15. When the cheesecake is cool and firm, remove from the springform pan and set on a serving plate.
16. For the chocolate ganache topping, put the chocolate chips in a heat proof bowl.
17. Microwave the heavy whipping cream until it just begins to boil, then pour it over the chocolate chips. Allow it to sit for 2-3 minutes, then whisk until smooth.
18. Pour the ganache onto the cheesecake and spread into an even layer. Allow to firm up a bit.
19. Add the chocolate ganache for the swirls to a piping bag fitted with a closed star piping tip and pipe swirls around the outer edge of the cheesecake. Leave a little space between swirls to add chocolate triangles.
20. Cut the chocolate bar into triangles and add to the cheesecake. Use remaining chocolate bar and a vegetable peeler to create little chocolate shavings over the top of the cheesecake.
21. Refrigerate until ready to serve. Store well covered. Cheesecake is best for 3-4 days.