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.
Serve plain or with blueberry sauce.