In a small bowl whisk together liquor of choice, brown sugar, vinegar or soy sauce, oil, mustard or lime, fresh herbs, garlic, and pepper.  Score the meat on both sides, and marinate in a re-sealable plastic bag, taking out all the excess air. Let sit in the fridge at least 4 hours, but for best results, overnight. 

Remove the London broil 20 minutes prior to grilling to bring the meat to room temperature. 

Discard marinade, as there was raw meat in it. 

Cook the meat in one of the following ways:

Grill: Preheat a grill, and grill the meat on an oiled rack set about 4 inches over glowing coals, turning once, for 9 to 10 minutes on each side, or until it registers 125 to 130 degrees on a meat thermometer for medium-rare meat. 

Let it stand for 10 minutes before slicing against the grain. 

Broil: Broil 4 inches from heat for 8-9 minutes on each side or until desired degree of doneness. 7. Let stand 10 minutes be- fore slicing against the grain. A London broil that goes for 8 minutes will cook to rare, while a steak that cooks for 10 minutes will cook to medium-rare to rare. For a medium-well steak, a full 12 minutes may be necessary. Broiling the steak for too much longer will likely dry it out.

Sear: Preheat your oven to 425°. 9. Get your cast iron skillet nice and sizzling hot with some olive oil, then sear the meat for 2-3 minutes on each side till it forms a nice, brown, crispy crust.   Finish in the oven for about 5 minutes. Rest for 10 minutes, then slice against the grain. 

The final piece in preparing London broil is slicing it thinly. Just like a piece of wood, meat has fibers that run through it, so when cooks talk about cutting across the grain, they are talking about cutting across those fibers. Look for the strands running left to right across the steak and cut vertically through them, making thin slices. 

Tip: Making shallow cuts on each side of the meat helps it cook up just right so the flavors of the marinade really get into the meat.