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How to Cook Costco Boneless Lamb Leg? [Recipe]

How to Cook Costco Boneless Lamb Leg
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During the holidays, there are only a few things that can match those gifts under the Christmas tree, and one of them is the dinner table with a roasted Costco boneless lamb leg. Preparing this meal takes a bit of time, but the meat is juicy, tender, and spicy, making it well worth the effort. The question is, how do you cook the boneless lamb leg from Costco?

To turn Costco Kirkland boneless lamb leg into a delicious meal, you can either roast or grill it. The cooking time for this meal depends on the size of the meat, and it is anywhere from 30 minutes to almost 2 hours. You can also use an instant pot to shorten the preparation. 

Holiday dinners can be stressful endeavors, especially if you lack the experience. Roasted boneless lamb leg is an elegant choice for such occasions and comes with a simple recipe. In the following paragraphs, I explain how to turn this meal into savory perfection, so keep reading.  

Cooking Instructions For Costco Lamb Leg

The best way to prepare a delicious meal with a boneless leg of lamb from Costco is to roast it. Before cooking, roasting, or grilling, you should season it with a lamb rub mixture of your choosing. 

Salt and pepper make the basic seasoning, but you can also add smoked paprika or cayenne, mint, garlic powder, rosemary, parsley, sage, onion powder, and some dried orange peel. If you get a cut of meat coated with fat, score it before you rub it in the seasoning. That way you’ll ensure that meat soaks in all of the spices.

Marinating the lamb leg before cooking, especially if you plan to grill it, will also enhance the flavor of the meat. Combine lemon juice, olive oil, salt, pepper, and garlic to make the marinade. Still, it is better to avoid marinating if you are cooking the meat in the oven because marinade can make it tough.

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In the Oven

Roasting the Kirkland boneless leg of lamb in the oven depends on the size of the package you purchase. According to most recipes, preheat the oven to 425 °F. 

After seasoning the meat, you can slice up some vegetables like potato, sweet potato, or carrot and add peas, shallot, or garlic cloves into a pan. Place the lamb leg over the vegetables and put it in the oven.

Cook the one-pound meat for 18 minutes for medium rare, 22 to medium, and 26 minutes to make the lamb leg well-done. To achieve the desired doneness, you can also use an instant thermometer — internal temperature should reach 145 °F for medium-rare, 160 °F for medium, and 170 °F for well-done.  

This cooking time is for one pound (16 oz) of meat. So try to adjust your baking time according to the size of your lamb leg.

Here is the table to help you out if you are aiming for medium at 425 °F (220 °C).

lbs of lamb legoz of lamb legkg of lamb legBaking time
1 – 216 – 320.4 – 122
3 – 448 – 641.3 – 1.845
4.5 – 672 – 962 – 2.855

On the Grill

If you are grilling the lamb leg, soak it in the marinade and refrigerate it for 30 minutes. Once you get it out of the fridge, leave it sitting at room temperature for an hour. When it warms up, place its fat side down on a grill as soon as the temperature reaches 300-350 °F. 

Sear the lamb leg for 4 minutes on each side. Move the meat to the cooler side of the grill, cover it and cook for around 45. While the leg is cooking, maintain the grill temperature at 300-350 °F. 

How to Cook Costco Boneless Lamb Leg

In the Instant Pot

An instant pot is a true timesaver. To cook a leg of lamb in it, you will need some seasoning, olive oil, chicken or beef broth and vegetables. Rub olive oil and seasoning into the meat, place it in a pot with another tablespoon of olive oil, and cook for 7 to 8 minutes on sauté mode.

Sear each side of the lamb leg for 4 minutes and add sliced vegetables with 2 cups of either beef or chicken broth. Press the “cancel” button, set the pot to “meat” or “stew” mode, and seal the pot. You should cook the meat for about 40 minutes. 


How to Cook Costco Kirkland Lamb Rack? [Recipe]

How to Reheat Costco Kirkland Lamb Leg?

If you have some Kirkland lamb leg leftovers, the best option is to reheat them in the oven. Preheat the oven to 325 F and wrap leftovers in a tin foil. Place the lamb leg in the oven and cook it for 15 or 20 minutes. 

You can also microwave the meat. Place leftovers in a microwave-safe dish with a lid. You should seal the dish and reheat it on high for 2 minutes.

What to Serve With Costco Lamb Leg?

The main course, such as roasted lamb leg, wouldn’t be complete without a side dish. The easiest option is to serve it with a tomato salad, roasted vegetables, or mashed potatoes, but there are many other exciting options.

A homemade BBQ sauce is always a good solution, but one of my favorites is a red wine sauce. Lamb meat gets along so well with red wine, and this sauce is pretty easy to make. With red wine, butter, beef stock, salt, and pepper, you will make it in no more than 10 minutes.

Grilled or fried asparagus in combination with some garlic and lemon zest is another great side dish for Kirkland lamb lag. If you prefer Brussels sprouts, you can use them instead of asparagus as well.

If you are in the mood for experimenting, try making broccoli and cheese sauce. Boil broccoli and use butter, milk, flour, shredded cheese, salt and pepper to make the white sauce. Pour the sauce over the broccoli, and there is another amazing side dish for your roasted lamb leg.

How Long Does a Costco Lamb Leg Last?

Unpacked Costco Kirkland lamb leg will last for 6 to 9 months in the freezer, but it is best to cook it within 3-4 months. If you keep the lamb meat in the fridge, cook it within 4 or 5 days.

Roasted leg of lamb will last 3-4 days in the fridge and for about 3 months in the freezer. Whether you cooked the meat or packed it in the freezer raw, avoid refreezing it.

How to Cook Costco Boneless Lamb Leg

Roasted Costco Boneless Lamb Leg

Author: Laura Bais
Hope you will like this recipe for Costco's lamb leg as much as I do! 🙂
5 from 5 votes
Prep Time 15 minutes
Cook Time 55 minutes
Resting Time 15 minutes
Total Time 1 hour 25 minutes
Course Main Course
Cuisine American
Servings 8 people
Calories 506 kcal



  • 88 oz Costco boneless lamb leg That's 5.5 lbs or 2.5 kg.
  • 1 tsp salt
  • tsp pepper
  • tsp Cayenne pepper
  • ¼ tsp onion powder
  • ¼ tsp garlic powder
  • ½ tsp smoked paprika
  • 1 spring rosemary

Side Dish

  • 2 tbsp olive oil
  • 3 carrots
  • 10 potatoes
  • 1 onion
  • 3 garlic cloves
  • tsp salt
  • dash of pepper


  • Preheat the oven to 425 °F (220 °C).
  • Mix all spices together, then use the mixture to season the meat. Rub it well so it absorbs all the flavors. Preferably, do this step the day before. If you are short on time, you can do that before cooking.
  • Cut the veggies into cubes (not too big so they can be done faster).
  • Season the veggies with some salt and pepper. Pour some olive oil and mix well.
  • Place the veggies on the bottom of one deep dish. Put it in the preheated oven uncovered for 55 minutes.
  • Note that if your lamb leg has around 2-3 lbs (32-48 oz; 1-1.4 kg), check the lamb after 45 minutes.
  • Leave lamb leg for at least 20 minutes before cutting. This way, the meat will be juicier.
  • Now slice the lamb and serve it with the side dish. Enjoy!


Serving: 1servingCalories: 506kcalCarbohydrates: 51gProtein: 46gFat: 13gSaturated Fat: 4gPolyunsaturated Fat: 1gMonounsaturated Fat: 6gCholesterol: 126mgSodium: 542mgPotassium: 1794mgFiber: 7gSugar: 4gVitamin A: 3910IUVitamin C: 55mgCalcium: 59mgIron: 6mg
Keyword costco lamb leg instructions, costco lamb leg recipe, lamb leg from costco, what to do with costco lamb leg
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