Lamb is a forgiving cut of meat to prepare, says "How to Cook Everything" author Mark Bittman. Whether it's medium-rare or well-done, it will still be juicy and flavorful. Determine how you'd like to serve the lamb and check it often while it is roasting, broiling, grilling or braising to make sure that it reaches your preferred level of doneness without being over- or under-cooked. Have a reliable meat thermometer on hand: the U.S. Department of Health and Human Services cautions it is impossible to check meat has reached a safe internal temperature without a meat thermometer.
Use the Correct Temperature
It's important to get the cooking temperature for your lamb right. Extremely high heat can make it tough, while too low and it won't be done when you're ready to eat. If you're roasting a whole leg of lamb, half a shank leg or a lamb shoulder, the American Lamb Board advises you heat the oven to 325 degrees Fahrenheit. This is true for boneless or bone-in legs or shoulders weighing between 3 and 9 pounds. To grill lamb chops, ribs, leg steaks, ground lamb burgers or kebabs, preheat a charcoal or gas grill to medium heat. For braised lamb shanks, roasts or chops, use a slow cooker on the lowest setting or put the meat in a Dutch oven and heat it in a 350 F oven.
Cook it Long Enough
Braised lamb requires the longest cooking time. Boneless stew meat or lamb shanks will need between 1 1/2 to 4 hours of stovetop or oven time before you can expect them to be done. In the slow cooker, these cuts will take around six to eight hours to cook. Expect a leg of lamb or shoulder roast to need 15 to 50 minutes per pound of meat, depending on the size of the cut, your desired level of doneness and whether it is bone-in or boneless. Grilled lamb steaks need about 14 to 18 minutes of cooking time, while lamb burgers may need only three minutes per side.
Check for Doneness
Use a fork to gauge the doneness of braised lamb, advises the American Lamb Board. When the meat is thoroughly cooked, a fork can easily shred it. Use your finger to estimate if roasted, grilled or broiled lamb is done to your liking. Press firmly on several sections of the lamb. If the meat gives easily but is firm and has cooked for the recommended length of time, it is probably medium-rare. A firmer texture and feel indicates more well-done meat.
Measure the Internal Temperature
Regardless of what cut of lamb you're preparing, it is not fully cooked and safe to eat until it has reached an internal temperature of 145 F. This temperature yields medium-rare meat. For medium lamb, wait until the meat has reached 160 F. Well-done lamb will register 170 F. Insert the meat thermometer into the thickest portion of the lamb cut, and make sure the probe is not touching any bones. Once the lamb is done, remove it from the heat and let it rest for at least three minutes before serving.