Preheat the broiler. On a baking sheet, broil the English muffin halves, cut side up, 4 inches from the heat for about 1 minute, or until golden. Turn the oven down to 375°. Butter the halves, stack and cut them into 1-inch cubes. Arrange the cubes in an even layer in four 8-ounce gratin dishes or other small shallow baking dishes.