Break eggs into a mixing bowl; add milk and beat until well blended. Add sifted flour and salt; continue beating until batter is smooth and thick. Bake in hot greased iron muffin cups or greased glass custard cups which are very hot. Bake at 450° for 20 minutes, then reduce heat to 350° and bake 15 to 20 minutes longer, depending on size. Serve right away. Make a small slit in each popover to allow steam to escape. Makes about 6 to 8 large popovers.