| Cream ricotta, cream cheese and sugar. Beat until creamy and light. Add butter, lemon juice, cornstarch, vanilla, flour and eggs and continue beating until well blended. Gently fold in sour cream. Preheat oven to 350 degrees F. Place a roasting pan of water on the bottom shelf of oven. Place ingredients into a well buttered spring form pan and place on the top shelf of oven. Bake for 1 hour. Turn oven off and leave cheesecake in the oven, without opening it, for 3 hours. Remove cake and place on wire rack until completely cool. Cover with plastic wrap and refrigerate overnight. Serve cold. | 
