Preheat the oven to 350 F and generously butter a 9-inch springform pan.In a mixing bowl, combine crumbs, sugar and butter. Press into bottom of pan.Set pan on a large sheet of heavy duty foil. Bring foil and up and around the side of the pan and press it tightly into the sides to make bottom water-proof. Do this (at least) twice.
Bake crust on center rack for 8-10 minutes.
Let cool.
Place one 8-ounce package cream cheese, 1/3 cup of the sugar, and the cornstarch in a large bowl. Beat with an electric mixer on low until creamy, about 3 minute, then beat in the remaining 3 packages of softened cream cheese.Increase the mixer speed to high and beat in the sugar, then beat in the vanilla, lemon extract ( if using) and heavy cream. Blend in the eggs, one at a time, stirring only until completely blended. Over-beating the eggs contributes to cracking, so don’t beat too much air into the batter at this point.Spoon the cheese filling on top of the crumb layer. Set the foil-wrapped pan in a large shallow pan and add hot water so that water comes about 1 inch up the sides of the springform pan.
Bake the cheesecake until the center barely jiggles when you shake the pan – 55 minutes to an hour.Cool the cake on a wire rack for 1-2 hours, then refrigerate until it’s completely cold — at least 4 hours or overnight.
Remove the sides of the springform pan and serve from pan bottom or transfer to a platter.
