Combine milk and flour in a small mixing bowl; mix well. Add eggs, one at a time, beating well after each addition. Add butter and salt to milk mixture; beat 5 minutes.
Heat a well-greased muffin pan in a 450° oven 3 minutes or until very hot. Spoon batter into muffin pans, filling two-thirds full. Bake at 425° for 20 minutes; reduce heat to 350°, and bake an additional 20 minutes. Remove popovers from pan, and serve immediately.