Finely grate the cheese. Cut cucumbers into thin slices. Spread slices of bread thinly with 1 tsp. mustard each. Cover 4 slices of bread with cheese, ham, cucumber and chips. Place 1 blank slice of bread on each slice and press the sandwich lightly together.
Heat 1 tablespoon of butter in a large frying pan. Fry 2 sandwich loaves in it over medium heat for 1-2 minutes on each side until golden brown. Remove and keep warm.
Fry the rest of the sandwich breads in the remaining butter as well. Cut all sandwiches in half and serve hot or cold.