Preheat oven to 320°F (160°C). Line and wrap an 8-inch round cake pan with foil to prepare for a water bath.

In a saucepan over low heat, melt cream cheese, butter, and milk until smooth. Let cool slightly.

Whisk in egg yolks one at a time, then sift in flour and cornstarch until batter is smooth. Stir in vanilla or lemon zest.

In a separate bowl, whip egg whites until frothy. Gradually add sugar and beat until soft peaks form.

Gently fold the meringue into the cream cheese batter in three additions, keeping the mixture light and airy.

Pour into prepared pan, tap gently to release large air bubbles, and place the pan in a larger tray filled with hot water.

Bake for 60 minutes, then reduce oven temperature to 300°F (150°C) and bake for another 15 minutes.

Turn off the oven, crack the door open, and let the cake cool slowly inside.

Once cooled, unmold carefully, dust with powdered sugar, and garnish before serving.