Heat 12-inch skillet over medium heat. Place 2 slices bread, buttered side down, in skillet and top each with half of the Cheddar cheese. Place remaining 2 slices of bread, buttered side up, on top of cheese. Cook 5 to 7 minutes, turning once, until golden brown on both sides and cheese is melted. Cool 5 minutes; cut each into 1-inch cubes. Serve with soup.