HEAT oven to 400°F.
HEAT lightly oiled baking sheet and cast iron skillet in oven.
SPREAD bottom halves of with mayo; spread top halves with mustard. Fill with pickles, cheese, roast pork and ham. Place on heated baking sheet. Brush tops with butter. Place heated skillet on tops of sandwiches to flatten slightly.
BAKE 5 min. or until sandwiches are crisp on both sides and heated through.