Butter both sides of the King's Hawaiian Bread.
Toast one side of the bread in a pan on the stove or on the grill if preferred. Add butter to the pan if desired.
Flip the bread, layer one slice of cheese, then proscitutto, then another slice of cheese, then apple, then another slice of cheese. At this point drizzle on some of the balsamic reduction (or you can save it for dipping), top with the other slice of bread.
Continue to cook until cheese is melty, about 1-2 minutes.
Cut in half if desired.
Serve with remaining balsamic reduction.
Enjoy!