Preheat oven to 320F; line round pan. Gently melt cream cheese, butter, and milk together until smooth; cool slightly.

Whisk in egg yolks, vanilla, and cake flour until smooth.

Beat egg whites and cream of tartar, gradually adding sugar, to soft peaks.

Fold whites into batter in thirds, retaining air.

Pour into pan; water-bath bake 55-60 minutes until tall and just set.

Cool gradually; chill 2 hours to firm before slicing.