Spread 1 t mustard on each slice of bread. Layer ham and cheese on 4 slices of bread. Cover with top half of bread slices, mustard side down. Spread tops of sandwiches with half of the butter.
Heat a nonstick skillet over medium-low heat. Add the sanwiches, buttered side down, in the pan. Spread the tops wth remaining butter and cook for 6 minutes, turning halfway or until brown. Cut in half and serve hot. Serve with additional mustard.