PREHEAT oven to 350ºF. Mix mayonnaise and mustard in serving bowl.
CUT each cheese slice in half. Top each of 16 of the crackers with 1 cheese slice, 1 ham slice and second cheese slice. Cover with remaining crackers. Place in single layer on baking sheet.
BAKE 6 to 8 min. or until cheese begins to melt. Serve with the mayonnaise mixture for dipping.