Preheat small skillet over low heat.

Spread butter or mayonnaise on one side of each slice of bread. Place 2 slices of bread in the skillet, butter side down. 

Place slices of cheese on the exposed side of bread and top with the remaining slices of bread, butter side out. 

Cook 4-5 minutes until bread is golden brown, flip sandwiches and cook opposite sides until golden brown.