Pour milk into 2 bowls; cover with aluminum foil. Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Bring water to a boil. Add bowls of milk, cover, and steam, about 5 minutes. Allow layer of skin to form on top of milk.

Flip up a corner of the milk skin and pour milk into an empty bowl, reserving the milk skin in the bowl.

Whisk egg whites and sugar together in a bowl; pour in the milk and mix well. Pour milk mixture back into the 2 bowls under the reserved milk skin. Cover with aluminum foil.

Steam milk mixture until set, about 15 minutes.