Preheat oven to 325 degrees F (165 degrees C). Move an oven rack to the middle of the oven.
Beat the cream cheese, ricotta cheese, and sugar in a large mixing bowl with an electric mixer until well combined. Beat in the eggs, one at a time. Add the butter, flour, cornstarch, and vanilla extract; mix until well combined. Fold in the sour cream and lemon juice. Pour the mixture into an ungreased 10-inch springform pan.
Bake in the preheated oven for 1 hour. Turn off the oven and leave the cheesecake in the oven for 2 more hours. Remove from oven and let cool completely. Run a thin spatula around the edge of the cheesecake before springing open the pan to remove. Serve at room temperature or cold; refrigerate leftovers.
