Heat a cast-iron skillet or griddle over medium-low heat. Lightly spread the inside of each English muffin half with butter. Arrange the muffins buttered sides out and build 4 sandwiches, each with a cheese slice, a tomato slice, some salt and pepper and another cheese slice. Place the sammies in the pan and cook, turning once or twice, until the cheese is melted and the muffins are golden-brown, about 8 minutes.