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 unsalted butter, and whole milk. Heat over low temperature, stirring continuously until the mixture is completely smooth and homogenous. Remove from heat and allow to cool slightly. Whisk in the fresh lemon juice and vanilla extract until thoroughly incorporated.

In a separate medium-sized bowl, whisk together the all-purpose flour, cornstarch, and salt. Set this mixture aside.

In a large mixing bowl, whisk the egg yolks with ¼ cup of the granulated sugar until the mixture becomes pale and slightly thickened. Gradually incorporate the cooled cream cheese mixture, whisking until fully blended and smooth.

Sift the reserved dry ingredient mixture into the yolk emulsion. Stir gently with a spatula until the batter is smooth and lump-free.

In a very clean, large bowl, use an electric mixer to beat the separated egg whites until soft peaks begin to form. Gradually add the remaining ¼ cup of granulated sugar while continuing to beat until stiff, glossy peaks are achieved.

Carefully fold one-third of the whipped egg whites into the cheesecake batter to lighten its consistency. Gently incorporate the remaining egg whites in two subsequent additions, using a spatula to fold until just combined, being careful to preserve the airiness.

Divide the prepared batter evenly among the lined or greased cupcake cups, filling each approximately three-quarters full. Lightly tap the muffin tin on the counter to release any trapped air bubbles. Bake for 20 to 25 minutes, or until the tops are lightly golden brown and a wooden skewer inserted into the center emerges clean.

Allow the baked cupcakes to cool in the muffin tin for 5 minutes before carefully transferring them to a wire rack to cool completely. If desired, dust with powdered sugar just before serving.