Take 2 pieces of sliced white bread. If you prefer you can toast the bread first.
Lightly butter one piece of bread.
Place a thin piece of ham on the slice of bread that was not buttered.
Place a piece of cheese (American, Cheddar, Swiss or any firm cheese of your choice) on the ham.
Cover the cheese with a leaf of lettuce.
Place the buttered piece of bread on the lettuce, buttered side down.
Enjoy.
If preferred, omit the lettuce and use toasted bread. Then microwave the sandwich for 10-15 seconds, enough to melt the cheese.