Gather bread slices, cheese (American, cheddar, or a mix), and butter or mayonnaise
Preheat a skillet over medium heat
Spread butter (or mayonnaise) on one side of each bread slice
Place one bread slice in the skillet with the butter side down
Add cheese in an even layer
Top with the second bread slice, butter side up
Cook until the bottom is golden brown, about 3–5 minutes
Flip carefully and cook until the other side is golden brown and the cheese is melted, about 3–5 minutes
Remove from the skillet and let rest 1 minute
Slice and serve