15 oz. Ricotta cheese
2 (8 oz.) pkgs. cream cheese
1 pt. sour cream
1 stick butter
1 1/2 c. sugar
3 tbsp. flour
3 tbsp. cornstarch
1 tsp. vanilla
3 eggs
3 tsp. lemon juice

Start with the first ingredient and add one at a time, beating well after each addition. Bake at 325 degrees for 1 hour in a 12 inch springform pan. Turn oven off and leave door closed for 2 additional hours. Top with whipped topping if desired.