The long-lasting debate over the perfect grilling method, driven by both renowned roast masters and "King of the Grill" apron-sporting dads, will likely never cease. Most do agree, however, on a few basic principles. London broil is a cooking technique that involves tenderizing and marinating a lean cut of meat prior to cooking. While grilling, handle the steak very little and be sure to cut the finished product against the grain at an angle. London broil is traditionally cooked for a short time over direct high heat, as overcooking will result in a tough, dry steak. Some grillers, however, prefer a slow-grilling method for a more tender result.
Before marinating, you may want to tenderize the steak with a meat mallet. This step is optional. If you do not own a meat mallet, the bottom of a heavy frying pan will also work. Lay the steak on a sturdy surface, such as a smooth, clean countertop or cutting board. Place a sheet of plastic wrap over the steak or slide the steak into a large resealable plastic bag. Pound the meat firmly a few times, but not so hard that you sacrifice the integrity of the meat.
Marinate the steak in a shallow covered dish or a large resealable plastic bag for one hour or up to an entire day. Store the meat in the refrigerator while marinating. To create a marinade, combine a mixture of wet and dry ingredients. For a tomato herb marinade, create a puree with shallots, one tomato, 1/4 cup red wine vinegar, 2 tbsp. chopped marjoram, 1 tbsp. chopped rosemary, 1 tsp. salt and 1/2 tsp. black pepper. If you prefer something with more of a kick, mix 1/2 cup each of olive oil and balsamic vinegar, 4 tbsp. Worcestershire sauce, 1 tsp. red pepper flakes, 1 tsp. black pepper, 1 tbsp. salt, 1/2 tbsp. oregano, 1/2 tsp. onion powder, 1 tsp. garlic powder and 1/2 tsp. cayenne pepper.
Prepare a gas grill with one burner on high heat and a second on low heat, or prepare a charcoal grill with one large pile and one shallow pile of burning coals. Sear the steaks for one or two minutes per side over high heat then transfer to the side with low heat. Cook the steaks for approximately eight minutes, flip using tongs, then cook for an additional eight minutes to medium doneness. A medium steak has brown edges, a pink center, and an internal temperature of 145 degrees F. The USDA does not recommend consuming beef cooked to temperatures lower than 145 degrees.
Allow the steak to rest for eight to ten minutes in its own juices. When slicing the meat, cut against the grain. This step is vital; cutting a London broil the wrong way can render hours of perfect prep work useless. Hold your knife perpendicular to the direction of the meat's natural fibers. Cutting against the grain creates a tender slice of meat with many short fibers -- rather than a few long, tough ones.