INGREDIENTS:
24 oz cream cheese, broken into pieces 
4 eggs, separated 
2 Tbsp vanilla extract (do not use artificial vanilla) 
1 cup sour cream 
1/4 cup brown sugar, or to taste 
1 lb chocolate chips 
1 lb graham cracker crumbs 
1/2 cup butter, melted.  

PREPARAZIONE:
Preheat the oven to 325 deg. F. 
Prepare the batter: place the egg yolks in a food processor for 5 seconds, then add the cream cheese and beat until smooth.
Add the brown sugar and vanilla and process for several minutes, or until the batter is very smooth. 
Add the sour cream, then beat the eggwhites and fold into the cheese mixture.
Set aside. 
Prepare the crust: soften butter and combine with graham cracker crumbs.
Mix until fully blended, e.g. they will form a ball when  queezed in your hand or by a spoon. 
Pat the crust into the sides and bottom of a springform pan about 9 inches in diameter. 
Spread a generous layer of chips on the bottom of the pan, and then pour the batter into the pan.
Add another generous layer of chips to the top of the cake. 
Place the filled pan into the preheated oven.
Baking time will vary from about 30 minutes to 2 hours.
Cooking time depends on whether you want a soft,  gooey "New York" style cheesecake (shorter) to a fluffy "souffle"-like cheesecake (longer). 
The longer you cook it, the fluffier it gets. 
When the cake starts to rise like a souffle, start checking to see if it is done.
It will just about double in volume, and should not flow over the sides of the pan.
If the cake shimmers like Jello when shaken, it is done. 
Alternatively, if a knife inserted comes out clean, the cake is overcooked: the knife should be very lightly coated with batter.