Lamb is generally the tenderest and most delicate of red meats, but some cuts are especially choice. One of those is the backstrap, or eye of loin. It's a cut featured prominently by butchers in Australia and the U.K., where lamb is prized, but seldom seen in the United States. As with beef tenderloin, this premium cut is usually reserved for special occasions. You'll find a number of recipes for lamb backstraps online, but most are variations on a few basic cooking methods.
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A Backstrap Primer
If you've ever had lamb loin chops, you've probably noticed that they look like tiny T-bone or porterhouse steaks. In truth that's exactly what they are, with a morsel of tenderloin on one side of the bone and a larger piece of loin on the other. That larger loin portion, corresponding to the strip loin on a beef carcass, is the lamb's backstrap. Butchers can cut just two backstraps from a given lamb, each weighing a pound or less, which largely accounts for their premium price.
You'll usually have to special-order backstraps from your butcher. Cutting a backstrap means getting no loin chops from that carcass; and few butchers willingly give up a high-demand cut without a guaranteed sale.
The lamb's loin has only a thin layer of protective fat to begin with, and that's removed when the loin is trimmed down to a backstrap. Since the cut is small and very lean to begin with, this means it's easily overcooked. Most recipes rely on quick cooking times to reduce this risk.
Grilling or Broiling
The whole lamb backstrap can be grilled or broiled in roughly the same length of time as a good steak. Brush the surface of the lamb lightly with oil or an oil-based marinade, then cook it over medium-high heat on your grill -- roughly 425 F -- or under the oven's broiler, 4 to 6 inches from the element. It should take just 3 to 5 minutes per side for the backstrap to reach medium-rare.
Roast a seasoned lamb backstrap for roughly 20 minutes at 425 F to reach medium-rare. Crust the lamb first in fresh herbs or a dry spice rub, if you wish, to add flavor and visual appeal. Breadcrumbs flavored with a French mixture called persillade -- parsley, garlic and a hint of lemon -- makes for an especially elegant crust.
The 'Sear-First' Method
The backstrap browns poorly when it's roasted, because of its short cooking time. Many recipes compensate for that by searing the backstrap first in a hot pan to create those rich, browned-meat flavors. Searing also means you can finish the lamb at a lower temperature, reducing the risk of overcooking it. While your oven is heating to 350 F, set a heavy skillet over a medium-high burner. Sear the top and bottom of the backstrap for about 2 minutes each, then transfer it to the heated oven. If you leave it in the skillet, it'll only need another 6 to 8 minutes. If you transfer it to a sheet pan, it'll take about twice as long.
You can cook the backstrap entirely in a large skillet, rather than finishing it in the oven. Use medium-high heat, and cook it for 4 to 5 minutes per side.
Doneness in meat is largely a matter of personal preference, but there are a few exceptions. Lamb backstrap is one of those, because of its leanness and delicacy. It's best when served at medium-rare -- 125 to 130 F -- and no more than medium, or 130 to 135 F. When cooked past medium, it rapidly becomes dry and chewy, losing its delicate flavor and texture.
The U.S. Department of Agriculture's official guideline calls for most meats to be cooked to 145 F, to maximize food safety. This would rule out serving meats rare or medium-rare, so most diners choose to ignore that guideline at least occasionally.