Spread mustard over four slices of bread. Layer each with a slice of cheese, ham and another cheese slice. Top with remaining bread.
Butter the outside of the sandwiches. In a large skillet over medium heat, toast sandwiches for 3-4 minutes on each side or until bread is lightly browned and cheese is melted. Remove to a cutting board; cut each sandwich lengthwise into thirds. Yield: 4 servings.