Spread softened butter evenly over one side of each slice of bread.
Place two slices of bread, buttered side down, in a skillet over medium-low heat.
Layer two slices of cheddar and one slice of American cheese on top of each bread slice in the skillet.
Place the remaining bread slices on top with the buttered side facing outward to close the sandwiches.
Grill for 4 to 5 minutes per side, flipping carefully, until the bread is golden brown and the cheese is fully melted before slicing and serving hot.