Preheat a skillet or griddle over medium-low heat
Butter one side of each bread slice
Place one slice of bread, buttered side down, in the skillet
Add cheese on top of the bread
Cover with the second slice of bread, buttered side up
Cook until the bottom is golden brown
Flip carefully with a spatula
Cook the other side until golden brown and the cheese is melted
Remove from the skillet
Let it cool briefly
Slice and serve