Preheat your oven to 320°F (160°C). Prepare a 12-cup muffin tin by lining it with cupcake liners or lightly greasing each cup.

In a saucepan over low heat, combine cream cheese, unsalted butter, and whole milk, stirring continuously until smooth and creamy (5-7 minutes). Remove from heat and cool slightly before blending in lemon juice and vanilla extract.

In a separate bowl, whisk together all-purpose flour, cornstarch, and a pinch of salt. Set aside.

In another bowl, whisk the egg yolks with granulated sugar until pale and creamy (3-4 minutes). Fold in the cooled cream cheese mixture.

Sift the prepared dry ingredients into the wet mixture and gently fold until just incorporated, being careful not to overmix.

In a clean bowl, beat the egg whites until soft peaks form. Gradually add the remaining sugar and beat until stiff peaks develop (4-5 minutes).

Gently fold one-third of the whipped egg whites into the batter, then fold in the remaining egg whites in two more additions.

Fill each cupcake liner about three-quarters full. Bake for 20-25 minutes until tops are lightly golden and a toothpick comes out clean.

Allow the cupcakes to cool in the tin for about 5 minutes before transferring to a wire rack. Dust with powdered sugar if desired.