Despite the young age of the lamb when it is processed for cooking, a lamb roast can be very tough and dry if it is not prepared properly. To ensure that your lamb roast is tender and juicy, you must take steps at each stage of the cooking process, from marinating the lamb to carving it, to keep it moist and buttery-soft. Your attention to these details will pay off, however, when your lamb roast turns out flavorful and melt-in-your mouth tender.
Trim away any fat and connective tissue on the roast. Lamb fat has an unpleasant flavor that will soak into the meat if it isn't removed before cooking, and it will become very solid and tough.
Place the lamb in a large, resealable plastic bag and pour in 2 cups of your preferred marinade. Classic marinade combinations for lamb include olive oil, lemon, and thyme, or simply use beef broth and a dry red wine. Place the bag in the refrigerator for 4 hours or overnight. The marinade will help the roast stay tender and juicy.
Take the bag out of the refrigerator and place it on the counter to warm to room temperature, or approximately 72 degrees Fahrenheit. The warming period will allow the marinade to finish penetrating the meat, as well as ensure that the lamb roast stays more tender as it cooks.
Cook the lamb roast slowly and at a low temperature using your preferred method of cooking. Lamb roasts can be roasted, grilled, slow cooked or braised as long as the heat is kept lower than 350 degrees Fahrenheit. The long, slow cooking will help the tough fibers of the lamb roast to break down, making the meat more tender.
Take the lamb roast off the heat source and allow it to rest for 15 minutes on a platter before you carve it into serving-sized portions. Allowing the roast to sit will give the hot juices time to cool slightly, which will keep them from running out when you carve the lamb.