Mix together ricotta cheese and cream cheese until creamy. Add, sugar and mix. Add eggs, 1 at a time, beating after each addition. Add flour, cornstarch and lemon juice to melted butter, then add to the first mixture. Add vanilla and sour cream.

Butter and flour a 9-inch springform pan. Pour in batter and bake at 325 degrees for I hour. Turn off the oven and keep the door closed for 2 more hours. Take out and cool to room temperature. Refrigerate. Two hours before serving, pour can of cherry or blueberry filling over the top of the cake. Yields: 1 cheesecake.