Heat the oven to 425 F. Generously coat 6 large metal or glass muffin molds with cooking spray. Heat the muffin molds in the oven for 2 minutes.
In a large bowl, add the milk, flour, salt and egg whites. Using an electric mixer, beat until smooth. Fill the heated muffin molds 2/3 full. Bake in the top part of the oven until golden brown and puffy, about 30 minutes. Serve immediately.