Preheat the oven to 300°F
Whisk cream cheese until it begins to get fluffy. Add in sugar, sour cream, cocoa powder and vanilla. Whisk until combine. Add in eggs one at a time, allowing each one to be mixed in as you go. Add melted chocolate and whisk until everything is mixed together.
Pour filling into the crust. Wrap the bottom of your pan in foil, but allow the top to be uncovered. Place in a larger pan and add water so that one half of your spring form pan is covered in water. Place cheesecake in the water bath into the oven. Bake for 1 hour 10 minutes.
After time has passed. Turn the oven off and leave cheesecake in the oven with the door closed for 30 minutes.
After 30 minutes has passed, remove from the oven and allow to sit at room temperature for 30 minutes more. Place in fridge for at least 5 hours to set, or overnight. Leave in the fridge until you are ready to serve.