Butter 12 standard size muffin cups or a popover pan. In a bowl combine eggs and salt. Using a whisk, beat lightly. Stir in milk and butter and beat in the flour just until blended. Do no overbeat. Fill each cup about half full and place in cold oven. Set temperature to 425 degrees and bake for 20 minutes. Reduce heat to 375 degrees and bake until golden, about 15 minutes longer. They should be crisp on the outside. Quickly pierce each popover with a thin metal skewer to release steam. Leave in the oven a couple of minutes for further crisping. Remove and serve at once. Makes 12.