Heat pan on medium-high heat. Spread margarine on 1 side of each slice bread.
Place one slice of bread, margarine side down in pan, then American cheese, then second slice of bread margarine side up. Cook for 2-3 minutes or until 1st side is golden brown. Flip and continue to cook until 2nd side is golden and cheese inside is melted.
While the 2nd side is cooking, top the first side is 1/2 of the cheddar cheese. It should melt a little and stick. When 2nd side is done, flip sandwich again and cook for just about a minute or until the cheddar is crisp. While that side is getting crisp, add 2nd half of cheese to the top. Turn one last time and cook for about 1 minute. The final amount of cheese will get crisp.