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

In a medium saucepan, melt cream cheese, butter, and milk over low heat until smooth, approximately 5-7 minutes.

In a separate bowl, whisk together flour, cornstarch, and salt.

In a large bowl, whisk egg yolks and granulated sugar until pale and thickened, about 2-3 minutes, then add lemon juice and cooled cheese mixture.

Sift the flour mixture into the wet mixture and stir gently until smooth.

Beat egg whites until soft peaks form, gradually adding remaining sugar until stiff peaks form, about 3-5 minutes.

Gently fold whipped egg whites into the batter in thirds, being careful not to deflate.

Spoon the batter into cupcake liners, filling each about 3/4 full, and tap the tin to remove air bubbles.

Bake in the preheated oven for 20-25 minutes or until tops are golden and puffed up.

Let cupcakes cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely before dusting with powdered sugar if desired.