To Mix Batter:
Arrange oven racks as close to the center of the oven as possible with at least 4 in. between them. Preheat oven to 350°F.
In a mixing bowl, beat cream cheese and sugar, preferably with flat beater, until very smooth (about 3 minutes). Beat in the cornstarch. Beat in the eggs, 1 at a time, scraping down sides of the bowl until smooth. Add the lemon juice, vanilla and salt and beat until mixed. Beat in sour cream just until blended.
Pour the filling into the prepared pans. Set the pans into the larger pans. Fill larger pans with at least 1 in. hot water.
Bake in preheated over for 50 minutes. Turn off the oven and allow the cakes to cool in oven without opening the door for 1 hour. Remove to racks and cool to room temperature (1 hour for the smaller layers, longer for the larger one). Cover with plastic wrap and refrigerate overnight.
Recipe requires a 5-quart mixer large enough to handle the batter in 2 batches. It can also be prepared in several batches in a food processor.
Note: Use glass measuring cups.