Preheat a non-stick skillet or griddle over medium heat
Spread margarine or butter on the side of every slice of bread (or spray the skillet with non-stick cooking spray if you prefer).
Place a slice of bread, the buttered side down, in the skillet.
Add the cheese slices on top of the bread.
Top with the second slice of bread, the buttered side up.
Then cook for 2-3 minutes, until the bottom slice of bread is golden brown and the cheese starts to melt.
Use a spatula to flip the sandwich over and cook for another 2-3 minutes on the other side until the bread is golden brown and the cheese is fully melted.
Remove the sandwich from the skillet and let it cool for a minute before cutting it in half and serving.