How to Cook a Leg of Lamb
There is some debate over which method yields the best results—slow cooking at low heat the entire time, or searing first on high heat and then slow cooking. James Beard in his American Cookery prefers the slow-cook-low-heat method (He rubs the roast with salt and pepper and cooks it at 325°F the whole time.). We generally get great results with the searing method, starting at high heat and then dropping the temp which is the method described in the following recipe. If you use the searing method, you will have ends that are more well done, and as you get closer to the interior, more rare. This way you have a variety to serve to guests. Another point where there are wildly varying opinions is the internal temperature that constitutes “medium rare”. I’ve seen references that range from 120° to 145°F. For this roast, I pull it out at 125°F. As it rests, the internal temperature continues to rise a few points as the meat continues to cook.
Use a Meat Thermometer
We like our roasted leg of lamb on the rare side of medium rare, and this roast was perfectly done to our taste. Clearly an accurate meat thermometer is essential, and it helps to insert the meat thermometer at different places into the deep interior of the roast to get a good read. A great way to keep tabs on how well the roast is cooking is to use a remote thermometer. This way, you can tell when the roast is done without having to open the oven door, avoiding the loss of heat that comes from doing that.
Let Lamb Roast Sit at Room Temp Before Cooking
The directions that follow in this leg of lamb recipe assume that you have let the roast sit at room temperature for an hour or two before roasting. If you are taking a roast and cooking it directly from the fridge, it will take longer to cook.
If you are cooking the roast directly in a roasting pan, start the roast at 450°F. After 20 minutes reduce the heat to 325°F.
1/2 cup orange juice
1 cup white wine
3 cloves garlic, minced
2 teaspoons fresh thyme (or 1 teaspoon dried thyme)
2 tablespoons fresh chopped rosemary (or 1 tablespoon dried rosemary)
1/4 teaspoon freshly ground pepper
For the Lamb Roast
1 (6-pound) leg of lamb, bone-in or boneless (a boneless leg should be tied up with kitchen twine by a butcher)
Salt and freshly ground black pepper
Marinate for several hours, or overnight, in the refrigerator. Remove the lamb, still in its marinade bag, from the refrigerator at least an hour (preferably two) before putting in the oven. This helps bring the lamb closer to room temperature before roasting. Note that this arrangement of racks and pans, with the roast sitting directly on the oven rack, will create a natural convection of heat in the oven, causing the roast to cook more quickly than if cooked the traditional method in a rack in a roasting pan. Generously salt and pepper all sides of the roast. Arrange the roast fattiest side up, so the fat will melt into the meat while the lamb cooks. Place the roast directly on middle rack of the oven. Place a roasting pan on a separate rack a rung lower to catch the drippings. You may also want to put some water in the bottom roasting pan, so the drippings fall into the water instead of burning in the hot pan and smoking up your kitchen. In general, estimate 10 to 13 minutes per pound for total cooking time (for rare), including that first 20 minutes at high heat. (Assuming you let the roast sit out for an hour or two before putting it in the oven. If it’s right out of the fridge, it will take longer to cook.) If you are cooking the roast directly in a roasting pan, start the roast at 450°F. After 20 minutes, reduce the heat to 325°F. Also, the shape of the roast will have an impact on the cooking time. Our roast was rather long and thin, so it cooked up fairly quickly. A thicker roast may take longer than expected. Remove the roast from the oven anywhere from 125°F to 135°F for medium rare. Lamb should never be cooked well done or it will be too dry. Serve with some mint chimichurri or homemade mint jelly on the side.
