1. In a blender or bowl, whirl or beat eggs, flour, milk, 1 tablespoon butter, and salt until smooth.
2. Generously brush six nonstick popover, custard, soufflé, or muffin cups (1/2-cup capacity; see notes) with butter; if using pans without a nonstick finish, coat with cooking oil spray instead. Pour batter equally into cups, filling them 3/4 to almost full. Set cups about 2 inches apart in a 10- by 15-inch rimmed baking pan.
3. Bake popovers in a 375° regular or convection oven until browned and puffy, 40 to 45 minutes. Pierce each popover in several places with a thin wooden skewer, then continue baking until very well browned and crisp, about 5 minutes longer. Remove from oven and run a thin-bladed knife between edge of each popover and cup to loosen. Lift popovers from cups and serve hot.
Nutritional analysis per popover.