General Guidelines
Roasting is usually done in a shallow, uncovered pan, often with the meat raised slightly on a rack to allow heated air to circulate completely around it. Roasting is the cooking method of choice for large or irregularly shaped pieces of meat if they are tender (or have been tenderized). A smaller cut, such as a chop, would dry out if roasted.
Lamb meat is naturally tender so most of the market ready cuts can be roasted with success. Of course, some cuts are more tender than others, but the shanks and the neck are the only cuts that must be cooked with moist heat methods. The shoulder cuts are often best when braised, but are also excellent when carefully roasted and are not overcooked. Shoulder from a young lamb is more likely to be tender. Leg, rib roast, (also known as rack of lamb including crown roast and guard of honor), and loin (including saddle) are ideal cuts for roasting. Baby, or hothouse, lamb is also roasted, but because the meat is so tender and has so little fat, special procedures should be followed.
In general, a roast should have a crisp brown surface and a juicy pink interior. This can be accomplished by searing the meat at high heat (450in the oven for a short time (usually 10 minutes) and then reducing the heat to 350for the remainder of the time. Typical cooking times (after the roast is seared) are 10 minutes per pound for rare meat, 12 minutes per pound for medium-rare, 15 minutes for medium, 20 minutes for well-done. These are approximate times, for average size, bone-in roasts at room temperature. Cold meat, directly from the refrigerator, or very large pieces, or boneless roasts will take somewhat longer. The only way to be sure that the meat has reached the desired doneness is to use a good quality rapid-response thermometer, inserted into the meatiest part, but not into fat or against a bone. It is a good idea to plan where you'll insert the thermometer as you prepare the roast.
Roast lamb should be allowed to rest, loosely covered with foil, for 10 to 30 minutes (depending on the cut) after removal from the oven. Cooking will continue during the resting period (the internal temperature will rise at least 5and as much as 10reaching the desired level of doneness. The rest period minimizes the loss of juice and allows the meat to become firmer, making carving much easier.
Roasting Temperatures
Lamb may be roasted at different temperatures, depending on the desired result:
High Heat: 400- 425(for the entire cooking time)
Roasting at high heat maximizes the brown crusty surface. This method should not be used on large pieces because the surface will dry out and may burn before the interior is cooked to the desired doneness.
Moderate Heat: 325- 350(for the entire cooking time)
Roasting at moderate heat maximizes juiciness and minimizes shrinkage. Leg roasts are often cooked this way.
Varied Heat: 425- 450followed by 325
Roast at 425- 450for an initial 10 – 15 minutes to brown the meat, then continue cooking at 325to the desired doneness.
Note: To prevent lean cuts from drying out while cooking, the meat may be rubbed with oil prior to roasting and/or basted with pan juices during roasting.