Beat the cream cheese with the granulated sugar and salt until it's soft and homogeneous. Every once in a while stop and scrape down the sides and bottom of the bowl to make sure that everything gets beaten in.
Add the cocoa powder and beat again. Then add the sour cream and melted chocolate and beat once again. Every once in a while stop and scrape down the sides and bottom of the bowl to make sure that everything gets beaten in.
Reduce the speed to a minimum and add one egg at a time. You know that you can add the next one when the previous one is incorporated. Finish to incorporate with a spatula if needed.
Pour the mix onto the cookie base and spread evenly.
Bake the cheesecake in a preheated oven at 180°C / 350°F. When you preheat the oven you want to have a baking pan with water at the bottom layer of your oven so the water preheats, too. If you forget to do it, you can add boiling water. The cheesecake goes on the level above it (not in the water). In this way, the cheesecake still cooks gently but you remove the risk of the water going into the cake.
As soon as it goes into the oven, reduce the heat to 150°C /300°F.
Bake the cheesecake for 1h15hmin-1h30min or until you see it starting to get golden on top and it jiggles like gelatin if you shake it slightly. Halfway through the cooking process, check that the water level hasn't dropped too much. If it has, fill it up with boiling water. When you remove it, it should giggle like set jello.
Wait for it to cool down completely and place it in the fridge overnight or for at least 8 hours.