Flank Steak benefits from a tenderizing marinade of balsamic vinegar, basil, Dijon mustard and garlic.
1. Combine marinade ingredients in small bowl. Place beef steak and marinade in food-safe plastic bag; turn steak to coat. Close bag securely and marinate in refrigerator 6 hours or as long as overnight, turning occasionally.
2. Remove steak from marinade; discard marinade. Place steak on grid over medium, ash-covered coals. Grill, covered, 11 to 16 minutes (over medium heat on preheated gas grill, 16 to 21 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally.
3. Season steak with salt and pepper, as desired. Carve steak crosswise into thin slices.