Gather bread slices, cheese slices (or shredded cheese), butter or mayonnaise, and a skillet
Preheat a skillet over medium heat
Butter one side of each bread slice
Place one bread slice, butter-side down, in the skillet
Add cheese on top of the bread
Place the second bread slice on top, butter-side up
Cook until the bottom is golden brown, about 2–4 minutes
Flip carefully and cook until the second side is golden brown and the cheese is melted, about 2–4 minutes more
Remove from the skillet and let rest 1 minute
Slice and serve