Japanese Cotton Cheesecake (Japanese Cheesecake)

Preheat your oven to 325°F (160°C).
Grease and line the bottom and sides of an 8-inch round cake pan with parchment paper. Wrap the outside of the pan with aluminum foil to prevent water from seeping into the batter during the water bath.
Melt the Cream Cheese Mixture:

In a medium saucepan, combine the softened cream cheese, milk, and butter. Heat gently over medium-low heat, stirring occasionally, until the butter and cream cheese are fully melted and smooth.
Remove from heat and stir in the vanilla extract. Set the mixture aside to cool.
Sift the Dry Ingredients:

Sift the cake flour and cornstarch into a separate bowl. This will help ensure there are no lumps in the batter.
Make the Egg Yolk Batter:

In a large mixing bowl, whisk the egg yolks and sugar together until pale and slightly thickened.
Add the cooled cream cheese mixture into the egg yolk mixture and gently stir to combine.
Gradually sift the dry ingredients into the batter and fold until smooth and well incorporated.
Whisk the Egg Whites:

In a separate clean bowl, beat the egg whites with cream of tartar using an electric mixer until soft peaks form.
Gradually add the sugar (for the egg whites) and continue to beat until stiff peaks form. The meringue should be glossy and hold its shape.
Fold the Mixtures Together: