Preheat oven to 500 ° F.
Blend cream cheese and sugar.
Beat in flour and vanilla.
Add eggs one at a time.
Stir in melted chocolate.
Add sour cream and blend.
Bake 12 minutes at 500° F.
Decrease heat to 200° F. Do not open the oven door!
Bake 60 minutes at 200° F. Again - don't open the door!
Remove from oven and cool 2-3 hours.
Refrigerate at least 8 hours.
Leave in the pan until you are ready to serve.