Place 2 slices Pullman or other white bread on a cutting board and spread mayonnaise on top side of each; this is key to a golden, delectable crunch. Heat a small skillet (nonstick, ideally) over medium. Slide in a dab of butter. When it melts, place 1 slice of bread, mayonnaise side down, in skillet; top with a few slices American cheese or cheddar; season with pepper. Top with second slice of bread, mayonnaise side up. When underside is golden brown, about 4 minutes, turn sandwich and add another dab of butter to skillet. Press down on sandwich to encourage even browning and to help melt cheese—be gentle, don't smash it. Cook until second side is golden brown and cheese is melted. Eat immediately, preferably with Campbell's Tomato Soup.