Preheat the oven to 320?F. Line a standard 12-cup muffin tin with paper cupcake liners or lightly grease each individual cup.

In a small saucepan, combine softened cream cheese, softened butter, and whole milk. Heat over low temperature, stirring continuously until smooth. Remove from heat and let cool slightly, then whisk in the lemon juice and vanilla.

In a medium bowl, whisk together flour, cornstarch, and salt. Set aside.

In a large mixing bowl, whisk egg yolks with ? cup sugar until pale and thick. Gradually mix in the cream cheese mixture until smooth.

Sift the dry ingredients into the yolk mixture and fold gently with a spatula until lump-free.

In a clean bowl, beat egg whites until soft peaks form. Gradually add remaining sugar and beat until stiff peaks form.

Fold one-third of the whipped egg whites into the batter. Gently fold in the remaining egg whites in two additions until just combined.

Divide the batter among the cupcake cups, filling each about three-quarters full. Tap the muffin tin on the counter to release air bubbles.

Bake for 20 to 25 minutes, until tops are golden brown and a skewer inserted comes out clean.

Cool in the tin for 5 minutes, then transfer to a wire rack. Dust with powdered sugar before serving, if desired.