London broil did not originate in britain, and it does not refer to a cut of beef (although some butcher shops call sirloin tip and top round london broil). Instead, it refers to a method of preparation: marinating and then broiling or grilling beef (usually a tougher cut like flank steak), and cutting it across the grain into thin strips to serve. The marinade used in this recipe is made with a mixture of red wine and balsamic vinegar, and top-round beef is used. The meat will need to marinate for 4 to 6 hours or overnight (and no longer than two days), so plan accordingly. All you really need to flesh out a great london broil dinner is a green salad and maybe some good artisan bread. But if you're really hungry, pull all out all the stops. Crumble some blue cheese into that green salad for an extra kick, or try a caprese salad, or put the sliced meat directly into the greens for a main-course salad.