Preheat the oven to 350°F and lightly grease a 9-inch springform pan.
In a large bowl, beat the softened cream cheese and drained ricotta until smooth and well combined.
Add the eggs, granulated sugar, melted cooled butter, lemon juice, and vanilla; mix until smooth.
Sift in the flour and cornstarch, then stir gently until just combined—do not overmix.
Fold in the sour cream until the batter is uniform.
Pour the batter into the prepared springform pan and smooth the top.
Bake for 1 hour at 350°F. When time is up, turn the oven off and leave the cheesecake inside with the oven door closed for 1 hour to cool slowly.
Remove the cheesecake from the oven and let cool completely at room temperature, then refrigerate until thoroughly chilled before serving.
Release and remove the springform sides, slice, and serve chilled with fresh fruit if desired.