Two inexpensive cuts of beef are top round and bottom round. They derive from the area of the cow called the beef round, which is a cow's rump and shank. London broil is not actually a cut of beef; rather, it is a technique for cooking tough types of beef.
Top round comes from the inside of the shank; it's the most tender round cut. Bottom round comes from the outside of the shank; it's the toughest round cut. Beef round tends to be inexpensive because these cuts are harder to cook than other cuts of beef.
Top round and bottom round cuts are suitable for braising, roasting, stews and other slow-cooking techniques. Top round may be used to make roast beef, while bottom round may be used to make rump roast. Round beef may be cooked London broil-style.
Making London Broil
Marinate top or bottom round steaks for 8 to 24 hours. Your marinade should include herbs, spices and acidic liquids such as wine and vinegar. Once your steaks have marinated, broil or grill them for 7 to 10 minutes per side.
Your marinade should include acidic liquids. This is because they help tenderize the meat by breaking down its connective tissues.
London broil is not actually a British dish; it originated in Philadelphia in 1931.