A common mistake made when cooking London broil steak is failing to marinade the meat beforehand, writes G. Stephen Jones on The Reluctant Gourmet. London broil does not refer to a cut of meat but instead a certain type of preparation that involves marinating, broiling and thinly slicing the beef.
London broil sometimes improperly refers to top round, a boneless cut of beef from the rear of the cow. It is very lean and needs to be tenderized with a marinade before it is grilled or broiled, and it is sliced before it is served. Medium-rare top round cooks for 4 to 5 minutes on each side when grilled, 5 to 6 minutes per side when seared and 6 to 7 minutes when broiled.
Any cut of meat can become London broil if it is prepared correctly. Start with an acidic liquid, such as soy sauce or vinegar, before adding other seasonings and flavors. The meat should marinade for up to 6 hours. After it has been cooked, it should be sliced thinly against the grain before being served.
London broil traditionally uses flank steak. Despite the name, London broil is most likely from North America, and its origins may be in Philadelphia.