Preheat your oven to 320°F (160°C) and line a 12-cup muffin tin with cupcake liners.

In a medium saucepan over low heat, combine the cream cheese, unsalted butter, and whole milk. Stir until everything melts together and forms a smooth mixture.

In a separate bowl, whisk together the all-purpose flour, cornstarch, and salt until well combined.

In a large mixing bowl, whisk the egg yolks, granulated sugar, and optional lemon juice until pale and slightly thickened.

Sift the dry ingredients into the wet mixture and gently stir until just smooth and lump-free.

In a clean bowl, beat the egg whites until soft peaks form, then gradually add in a little sugar until stiff peaks form.

Gently fold a third of the beaten egg whites into the cupcake batter, then gradually fold in the remaining egg whites.

Evenly pour the batter into the prepared cupcake liners, filling them about three-quarters full.

Place the muffin tin in the oven and bake for 20-25 minutes, or until the tops are golden and slightly puffed.

After 5 minutes of cooling, transfer the cupcakes to a wire rack to cool completely. Dust with powdered sugar before serving.