Preheat your oven to 350°, and grease a 9- inch springform pan Mix your cream cheese and ricotta cheese until combined, then stir in the eggs, sugar, lemon juice, vanilla, cornstarch, flour, and butter. Add the sour cream last. Stir to combine.
Pour into your greased springform pan. Bake for one hour, then turn off the oven. Leave the cheesecake in the oven for an additional hour. Cool, then move to the refrigerator.
The cheesecake should be fully chilled before serving.