Preheat the oven to 320°F (160°C) and line a muffin tin with paper liners.

In a heat‑proof bowl over simmering water, combine cream cheese, butter, and warm milk until smooth.

Remove from heat and stir in lemon juice and vanilla extract.

Sift in cake flour and cornstarch and whisk until incorporated.

Add egg yolks and mix until just combined.

In a separate bowl, beat egg whites and cream of tartar until frothy, then gradually add sugar until stiff peaks form.

Fold one‑third of the meringue into the batter to lighten, then fold in the rest carefully.

Spoon batter into liners and place the muffin tin in a roasting pan. Add hot water to halfway up the tin.

Bake for 25–30 minutes until lightly golden and set.

Cool in the oven with the door ajar for 15 minutes, then transfer to a rack to cool completely.