Brush one side of each bread slice with 1/2 tablespoon butter. Lay two slices, buttered side down, on a clean work surface. Spread 1 teaspoon honey mustard on both slices. Top each slice with 1 slice cheese, 2 slices of ham, a second slice of cheese, then the other two bread slices, buttered side up.
Heat a large pan or griddle over medium heat until hot. Place sandwiches in pan, reduce the heat to medium-low and cook until the undersides are golden brown, 2-3 minutes. Flip the sandwiches and brown the other side, 2-3 minutes more. Sandwiches should be golden and crisp on the outside and melted inside.
Cut sandwiches in half and serve with Baked Potato Soup.