How to Roast a Boneless Leg of Lamb

Nothing could be easier than roasting a boneless leg of lamb for dinner. Growing up, I remember Sunday dinners of roast leg lamb served with roasted potatoes and mint jelly and eating the leftovers during the week. We roasted a lamb this week for dinner, had leftovers the next night and I’ve been making sandwiches for the last couple of days.

Buying a Leg of Lamb

There are basically three ways you can buy a leg of lamb and each has its advantages. There are actually more than these three cuts, but for simplicity, let’s go with three. By the way, even though a lamb has 4 legs, only the 2 back legs are referred to as “leg of lamb”.

Bone-in leg of lamb is usually a little cheaper, cooks faster than boneless, gives you a bone for making stock for lamb stew and because of the bone is a little juicier and has more flavor. A domestic leg of lamb weighs about 7 to 8 pounds.

Boneless leg of lamb with the bones removed is perfect for roasting and easy to carve. You can find it at your supermarket with the thin membrane (called fell) removed and the meat wrapped in a net to hold it together and keep its form.

Whether you buy the whole leg and have it boned or just the top half (sirloin half) or bottom half (shank half) really depends on how many you are serving and your personal preferences.

The sirloin half (consisting of the top of the leg and part of the hip) is meatier and more tender than the shank half (consisting of the lower part of the leg) which is chewier because it has more connective tissue. However, cooked properly, the connective tissue breaks down to be more tender and gelatinous with lots of flavor.

Butterflied leg of lamb is just a boneless leg that has been cut down the center in half but not completely through. The halves are opened to lay flat making the meat easier to grill or broil but can also be stuffed and rolled.

American (Domestic), New Zealand or Australian Lamb?

I will start off by quoting The Complete Meat Cookbook by Bruce Aidells and Denis Kelly, “When it comes to flavor, tenderness, and overall quality, you can’t beat lamb from the United States, especially California, Colorado, and Vermont”

No matter what country you buy it from, try to get it fresh. A lot of the lamb coming over from Australia and New Zealand is frozen although more and more is coming over fresh. You will find the New Zealand and Australian lamb to be smaller in size and weighing less.

One of the big differences between American lamb and “Down Under” lamb is diet. While the New Zealand and Australian lamb are raised almost exclusively on grass, American lamb is “finished” on a grain, which may be the reason the meat is a bit milder.

Roasting Technique

I said roasting a leg of lamb is simple but first you have to decide what method of roasting you want to follow. Everyone has his or her own ideas on roasting meat these days. If you follow Barbara Kafka’s technique as described in her informative Roasting – A Simple Art, you start at 500ºF for 10 minutes, then lower heat to 425º until the meat is at the desired temperature.

If you are a fan of Bruce Aidell and Denis Kelly in their Complete Meat Cookbook, you might roast the lamb at 350ºF the entire time until desired temperature.

Me, I like both these methods but I’m also a fan of Julee Rosso & Sheila Lukins’ The New Basics Cookbook. I broke my teeth on this book when I first started learning how to cook and go back to it often as a reference. I think it is one of the most important cookbooks you can own when starting out.

They give you all sorts of choices; bone in, bone out, high-heat, low-heat, stuffed, not stuffed but we went with starting at 450ºF for 30 minutes and then reducing the heat to 375ºF until our desired internal temperature.

You really can’t go just by time because there are so many factors that can effect the eventual temperature including the weight of the meat you are cooking, how tightly it is tied, is it stuffed or not, how hot your oven is really cooking at, how long you let it rest - that kind of stuff.

What is the desired internal temperature?

Lamb is naturally tender so you don’t want to over-cook it. Most chefs will tell you to cook and serve it rare. In our house, we like it more medium especially when serving it to the kids. If I was serving the lamb to guests who like it rare, I might pull it out rare, cut off a piece of the meat and continue cooking the rest for a few more minutes until medium. The question is what temperature is rare, medium-rare and medium?

If you look through 10 different cookbooks, you may find 10 different temperature ranges for each level of doneness.   For example, The Complete Meat Cookbook says rare is 125ºF to 130ºF, medium-rare at 130ºF to 140ºF, and medium at 140ºF to 150ºF.

The New Basics Cookbook sees rare at 135ºF to 140ºF and medium at 150ºF to 155ºF.

And then there is the USDA Recommendation. They see rare at 140ºF, medium-rare at 150ºF, and medium at 160ºF. Most chefs would tell you an internal temperature at 160 is well done and too dry.

The answer is to experiment and figure out what temperature is best for you. Once you know that, you can cook it anyway you want knowing just when to remove it from the oven.

Resting & Thermometers  

A mistake many home cooks make and certainly affects the final temperature is resting time. As with all roasts, you want to remove them about 5 degrees before they reach the desired ideal internal temperature. This is to allow the juices to redistribute throughout the entire piece of meat.

As the meat rests, it will continue to cook about 5 more degrees, the juices will redistribute and you will end up with a more flavorful, tender result. Never remove the meat from the oven and start carving. Give it a short and meaningful rest.

As for thermometers, they are not all alike and if you have an old meat thermometer that has been in your kitchen drawer for years, it may need to be recalibrated or thrown out and replaced.

We used our old meat thermometer and pulled the meat out at our desired temperature of 140ºF and then tested it with an instant thermometer to see that it read 150ºF. After resting, it ended up at about 155ºF and was ok for us, but you can see how important it is that your thermometer is accurate. Then again, maybe my old thermometer was really the accurate one. I’ll have to test them in boiling water.

Roast Boneless Leg of Lamb 

You really don’t have to do too much to have good results with a boneless leg of lamb. We added some herbs to it but you could just season it with salt and pepper like my mother did and have a great outcome.

We used the pan juices, along with some of the herbs that fell off when removing the netting and a cup of demi glace to make an incredible pan sauce that even the kids raved about. We served the lamb with my dad’s homegrown new potatoes and steamed artichokes.

Here’s what we did:

Ingredients

1 boneless leg of lamb (about 4 to 5 lbs)
2 tablespoons fresh rosemary
2 tablespoons fresh thyme
2 tablespoons fresh oregano
4 cloves garlic
Olive oil
Salt & pepper

How to Prepare Roast Boneless Leg of Lamb with Fresh Herbs

Preheat the oven to 450ºF.

While the oven is heating, finely chop the herbs and garlic or use a food processor like we did.

Rub some oil on all sides of the lamb and season with salt and pepper. Spoon the herb/garlic mixture on the topside of the lamb and spread it out.

Place the lamb into a shallow roasting pan and roast for 30 minutes at 450ºF. Reduce the oven temperature to 375ºF and continue cooking until you reach the desired doneness as discussed above.

Let the roast rest for 5 to 10 minutes until the internal temperature reaches idea temp.

While the roast is resting, now is a great time to make some pan sauce. We poured the juices from the bottom of the roasting pan into a saucepan, added a cup of demi glace and some of the herbs that fell off the roast when removing the netting. Let the sauce reduce until it is thick enough to coat a spoon.

Ideally you would strain the sauce before serving, but we usually don’t and it tasted great. Chefs have told me that straining makes a big difference so I need to incorporate that technique into my repertoire.

We didn’t do this, but I bet a couple of tablespoons of mint jelly added to this sauce would be incredible.