Coat inside of a 10 inch springform pan generously coat inside of pan with butter.
Preheat oven to 300º F.
Beat cream cheese and butter until smooth.
Add eggs one at a time.
Add sour cream.
Add sugar, cornstarch and vanilla- beat 2 minutes.
Pour into springform pan.
Fill a small cake pan with hot water and place in oven next to the springform to add moisture.
Bake for 1 hour 15 mins. or until just has only a slight jiggle in the center.
Shut oven off and Crack open door for 30 mins.
Then remove to counter to cool.
Cover and refrigerate until well chilled.
I like to slice and then pop the slices in the freezer so they are always on hand.
When serving, drizzle on the hot chocolate which will set immediately like a magic shell!