Tightly wrap 2 layers of aluminum foil around the outside of a 10 inch springform pan covering bottom and sides.
Generously coat inside of pan with butter.
Preheat oven to 300º F.
Using an electric mixer with paddle attachment, beat cream cheese and butter until smooth.
Add eggs one at a time until blended.
Add sour cream and mix until smooth.
Add sugar, cornstarch, vanilla and lemon juice, beat until smooth, about 2 minutes.
Pour into springform pan and place in a roasting pan large enough to prevent sides from touching.
Place into oven and carefully pour boiling water into roasting pan to reach halfway up sides of springform pan. (be careful not to splash any water onto cake)
Bake for 2 hours, or until cake is lightly browned on top. My oven is a convection oven, so bake time in regular oven may be longer.
Remove from water bath (bain-marie), remove foil and cool completely at room temperature before unlatching and removing rim.
Cover and refrigerate until well chilled (best to leave chill overnight). Cake must be well chilled to set properly.
Serve plain or with berries and whipped cream or even caramel sauce.