Preheat your oven to 320°F (160°C) and line a 12-cup muffin tin with cupcake liners. Fill a large baking pan with about 1 inch of hot water for a water bath.

In a heatproof bowl over simmering water, combine cream cheese, stirring until smooth (about 5 minutes). Allow to cool slightly, then whisk in egg yolks one at a time and lemon juice.

Sift together cake flour and cornstarch. Fold these dry ingredients into the cream cheese mixture until smooth with no lumps.

In a separate bowl, whip egg whites with cream of tartar until foamy. Gradually add sugar while beating until soft peaks form, and the meringue looks glossy.

Gently fold one-third of the whipped meringue into the cream cheese mixture to lighten it, then fold in the remaining meringue in two additions without deflating.

Divide the batter evenly among the cupcake liners, filling them about 80% full. Place muffin tin in the preheated water bath and bake for 25-30 minutes until tops are lightly golden.

Turn off the oven and leave the cupcakes inside for 15 minutes with the door slightly ajar. Transfer to a wire rack to cool completely, then refrigerate for at least 1 hour before serving.