Preheat oven to 375 degrees. Grease well with melted butter or vegetable oil eight 6-ounce custard cups or twelve 2 1/2- by 1 1/4-inch muffin-pan cups. Set custard cups on jelly-roll pan for easier handling. In medium bowl, with mixer at low speed, beat eggs until frothy; beat in milk and melted butter until blended. Gradually beat in flour and salt. Or, combine all ingredients in blender; blend until smooth. Pour about 1/3 cup batter into each prepared custard cup or fill muffin-pan cups half-full. Bake 50 minutes, then quickly cut a small slit in the top of each popover to let out steam; bake 10 minutes longer. Immediately remove popovers from cups, loosening with spatula if necessary. Serve hot. Makes 8 medium or 12 small popovers.