Combine TABASCO® Steak Sauce, shallot, garlic, vegetable oil, rosemary, and TABASCO® Sauce in a 12 x 8-inch baking dish and mix well. Add flank steak and turn to coat both sides. Cover and marinate in refrigerator at least 2 hours or overnight; bring to room temperature before grilling.
Preheat grill or broiler to medium-high. Place steak on rack in grill or broiler pan. Cook 12 to 15 minutes, turning midway, for medium-rare or until desired doneness. Serve with additional steak sauce and garnish with rosemary sprigs, if desired.
Makes 6 to 8 servings.