Score the steak on both sides in a shallow crisscross pattern to help it absorb the marinade.
Combine all marinade ingredients in a gallon size storage bag.
Place the steak in the marinade and refrigerate for a minimum of two hours. For best results allow the meat to marinate for 24 hours.
About an hour before you are ready to grill the meat, remove it from the refrigerator and allow it to come to room temperature.
Preheat the grill to medium-high, 400 degrees F.. Brush the grill rack with vegetable oil to keep the meat from sticking.
Remove the London Broil from the marinade and place on the grill rack. Reserve the marinade and set aside.
Grill the meat on the first side for about four minutes. Flip the steak and cook on the other side for about 4 minutes. The amount of time it will take your steak to cook depends on the thickness of the steak and the temperature of the beef. Thicker steaks will take more time, thinner steaks will take less time.
Remove the steak from the grill when the internal temperature of the beef registers 125 degrees on an instant-read meat thermometer. Cover it loosely with a piece of aluminum foil and let it rest for at least ten minutes. The internal temperature of the beef will continue to rise to 130 degrees F which is medium-rare.
While the steak is resting, pour the reserved marinade into a small saucepan over medium-high heat. Bring it to a boil and then reduce the heat to low. Let the marinade simmer for about 5 minutes.
To serve the London Broil, use a sharp knife and slice the steak across the grain or across the width, angling down from the top into paper-thin slices.
Arrange the slices on a platter and top with the reserved marinade and fresh rosemary. Serve immediately.
I highly recommend fresh rosemary for this marinade. However, if all you have is dried, by all means, use it. But, only use 1-1/2 tablespoon of dried. The flavor is much more concentrated in dried herbs.In a pinch, you can substitute real maple syrup (not imitation maple pancake syrup), corn syrup, or brown sugar for the honey in this recipe. I like to keep things simple when serving London Broil and usually pair it with a baked potato, salad, or a Caprese salad and a nice glass of pinot noir. If your steak is thicker or thinner than 1-1/2 inches, it will take longer or less time. We cooked a 2-inch London broil recently and it took 20 minutes to come up to temperature. The secret to success with this cut of meat is to slice it as thinly as possible across the grain or across the width, angling down from the top. The thinner the better! Paper-thin is what you are aiming for.