Preheat the oven to 350°F. Grease the bottom and sides of a 9-inch springform pan with softened butter or cooking spray.
In a large bowl, use an electric mixer or stand mixer to beat the cream cheese and ricotta together until smooth.
Add the sugar, eggs, lemon juice, vanilla, cornstarch, flour, melted butter, and sour cream. Mix until just combined and completely smooth—do not overmix or whip too much.*
Pour the batter into the prepared pan and smooth the top. Gently tap the pan on the counter a few times to release any air bubbles.
Bake for 1 hour. The center of the cake will still be quite jiggly.
Turn off the oven and leave the cake inside with the door closed for 1 additional hour.
Remove from the oven and let cool completely at room temperature. Then chill for at least 8 hours (overnight is best).
Release the springform pan and carefully remove the cheesecake. If needed, dip a knife in hot water and run it around the edges to help loosen it.
Slice and serve with fresh berries, whipped cream, and/or a dusting of powdered sugar.
