1/2 cup sifted cake flour
1 teaspoon baking powder
Pinch of salt
3 extra-large eggs (3 separated, 2 for cream cheese filling)
1/3 cup plus 2 tablespoons sugar
1 teaspoon plus one tablespoon pure vanilla extract
3 drops pure lemon extract
1/4 teaspoon cream of tartar
4 8-ounce packages of cream cheese, at room temperature, for cream cheese filling
1 2/3 cups sugar, for cream cheese filling
1/4 cup cornstarch, for cream cheese filling
3/4 cup heavy whipping cream, for cream cheese filling
For the Thin Sponge Cake Layer: Preheat the oven to 350 degrees F and generously butter the bottom and sides of a 9-inch springform pan (preferably a nonstick one).
Wrap the outside with aluminum foil, covering the bottom and extending all the way up the sides.
In a medium sized bowl bowl, sift the flour, baking powder, and salt together. Set Aside.
Beat the egg yolks in a large bowl with an electric mixer on high for 3 minutes. With the mixer running, slowly add 1/3 cup of sugar and beat until thick light-yellow ribbons form, about 5 minutes more.
Beat in the 1 tsp of vanilla extract along with the lemon extract.
Sift the flour mixture over the batter and stir it in by hand, just until no more white flecks appear. Now, blend in the melted butter.
In a clean bowl, using dry beaters, beat 3 eggwhites and the cream of tartar together on high until frothy. Gradually add 2 tablespoons of sugar and continue beating until stiff peaks form (the whites will stand up and look glossy, not dry).
Stir about 1/3 cup of the egg whites into the batter, then gently fold in the remaining whites. Don't worry if you still see a few white specks, as they'll disappear during baking.
Gently spoon the batter into the pan. Bake the cake until just the center of the cake springs back when lightly touched, only about 10 minutes (watch carefully!).
Let the cake cool in the pan on a wire rack while you make the cheesecake filling. Do not remove the cake from the pan and leave the oven on.
To make the Cream Cheese Filling: place one 8-ounce package of the 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 minutes, scraping the bowl occasionally. Beat in the remaining 3 packages of cream cheese.
Increase the mixer speed to high and beat in the remaining 1 1/3 cups of the sugar, then beat in 1 tbsp vanilla extract. Blend in 2 eggs, one at a time, beating the batter well after adding each one.
Blend in the heavy cream. At this point, mix the filling only until completely blended. Be careful not to overmix the batter.
Gently spoon the cheese filling on top of the baked sponge cake later. Place the springform pan in a large shallow pan containing hot water that comes about 1 inch up the sides of the pan.
Bake the cheesecake at 350 degrees F until the center barely jiggles when you bake the pan, about 1 hour and 10 minutes.
Cool the cake on a wirerack for 1 hour. Then cover the cake with plastic wrap and refrigerate until it's completley cold, at least 4 hours or overnight. Remove the sides of the springform pan. Slide the cake off the bottom of the pan onto a serving plate.
Or if you wish, simply leave the cake on the removable bottom of the pan and place it on a serving plate. If any cake is left over, cover it with plastic wrap and store in the refrigerator.