Lemon herb butter: Beat 1/3 cup soft butter until fluffy; gradually beat in 1 1/2 T lemon juice until well combined. Mix in 3 T each finely chopped parsley and watercress, 1 tsp. Worcestershire sauce, 1/4 tsp. Tarragon and dash white pepper. Shape into a roll or cube, wrap, and chill to blend flavors. Place steak in shallow dish. In a covered jar or blender, shake together oil, wine, worcestershire sauce, soy sauce, mustard, garlic, salt, sugar, and savory. Pour over steak, turning to coat well. Cover and refrigerate, 8 hrs. Or more, turning once or twice. Remove steak, reserving marinade. Place on a rack in a broiling pan. Broil about 4" from heat, until well browned (about 6 minutes per side for rare), brushing occasionally with marinade. Slice thinly, cutting diagonally. Serve topped with thin slices of lemon herb butter. Garnish with watercress. Tips: Flank steak will be most tender if cooked only to rare or medium rare stage of doneness. Cooked more, it tends to become rather tough. You can substitute 2 T cider vinegar for 1/4 cup dry red wine.