Preheat the oven to 350 F and generously butter a 9-inch springform pan.

I would wrap outside of pan with foil as mine leaked a bit!

Sift the cake flour, baking powder, and salt together in a medium sized bowl and set aside.

Beat the egg yolks together in a large bowl with an electric mixer on high for 3 minutes.

Then, with the mixer still running, gradually add the 1/3 cup of sugar and continue beating until thick light-yellow ribbons form in the bowl, about 5 minutes more.

Beat in the vanilla.

Sift the flour mixture over the batter and stir it in by hand until mo more white flecks appear.

Then blend in the butter.

In a clean bowl, using clean dry beaters, beat the egg whites and cream of tartar together on high until frothy.

Gradually add the remaining 2 tablespoons sugar and continue beating until stiff peaks form (the whites should stand up in stiff peaks, but not be dry).

Stir about 1/3 cup of the whites into the batter, then gently fold in the remaining whites.

Gently spoon the batter into the pan.

Bake until just set about 13-15 minutes.

Cool in the pan on a wire rack while you make the cheesecake filling which will go right on top of this.

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, then beat in the remaining 3 packages of the cream cheese.

Increase the mixer speed to high and beat in the remaining 1 1/3 cups of the sugar, then beat in the vanilla.

Blend in the eggs, one at a time, beating the batter well after each one.

Blend in heavy cream.

Gently spoon the cheese filling on top of the baked sponge cake layer.

Keep foil on outside of springform pan and place pan in a large shallow pan containing hot water that comes about 1 inch up the side of the pan.

Bake the cheesecake until the center barely jiggles when you shake the pan, about 75-85 minutes.

Cool the cake on a wire rack for 1 hour.

Then cover the cake with plastic wrap and refrigerate until it's completely cold, at least 4 hours or overnight.

Beat all ingredients on high in mixer until thick.

Pipe or spread onto cold cheesecake and chill again.

Remove side ring of pan carefully.

Combine all ingredients in microwave safe dish and heat until melted. Let cool quite a bit before pouring onto cake over the cream. Chill until serving time.