Sprinkle peppercorns over both sides of steak, pressing in lightly. Place steak on a lightly greased grill 4 to 6 inches above a solid bed of hot coals. (Or place steak on a rack in a broiler pan and broil about 3 inches below heat.) Cook turning once until done to your liking when cut (about 10 minutes for medium-rare) Meanwhile, melt butter in a 3 to 4 cup pan on cooler part of grill (or over low heat); stir in mustard and vermouth. Transfer steak to a rimmed platter; pour sauce over and around steak. Cut into thin slanting slices, swirling pieces in sauce. Offer with bread slices.