Preheat oven to 425 degrees. Generously grease 12 deep custard cups (5 oz. each) or 16 medium muffin cups.
Sift flour and salt together, set aside. With a hand mixer, beat eggs until light and fluffy, add flour and 1 cup milk. Continue to beat slowly until all flour is moistened. Gradually add remaining milk and melted butter, beat until smooth (about 1 to 2 minutes).
Fill custard or muffin cups ½ full. Bake for about 40 minutes or until deep golden brown. Serve immediately from pan.
Cook's Note: It is important that the oven door not be opened during baking, a blast of cold air on the popovers before their walls are set may make the steam condense and the walls collapse.