This is the inside leg muscle, opposite the Bottom Round. Top Round Steaks are thick slices cut crosswise from the roast. Thinner slices are called simply Round Steaks. The Top Round Steak is sometimes called a London Broil, but that is the name of a menu item, not a cut, and it is more commonly from the Flank.
This cut is very lean. Though not as tough as the Bottom Round, it is not a tender cut. Taking a thick "steak" like this and grilling it or broiling it, well, you'd better have a sharp steak knife and strong teeth. The photo specimen, labeled as Top Round - Lond Broil, was 10 inches long, 6.5 inches wide, 1-1/4 inches thick and weighed 2 pounds 12 ounces.
More on Cuts of Beef.
When used for London Broil (a preparation completely unknown in England) it is first marinated for several hours, then seared over very high heat (grilled or broiled). For serving, it is sliced very thin across the grain.
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