Slow Roast Leg of Lamb (Bone-In or Boneless)

4.74 from 19 votes

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Tender leg of lamb is just the thing for a cold winter’s day. Roasted with vegetables, herbs, and seasonings, it becomes impossibly moist, juicy, and flavorful. Serve this fall off the bone lamb with mashed potatoes for a world class dinner this Sunday (or any day)!

tongs pulling fall apart tender Slow Roasted Leg of Lamb


Cooking with lamb seems daunting, but it certainly doesn’t have to be. My slow roast leg of lamb recipe is fool-proof. With simple seasonings and ingredients, the hardest part is having to smell this delicious roast while it slowly cooks in the oven!

When I make this dish, I use a 5.5 lb bone-in leg of lamb as I feel the bone adds so much flavor. However, not every time I want this is one available! So, I have included instructions for both bone-in and boneless leg of lamb so that you can prepare this meal based on your favorite cut of meat — or whatever you are able to find in the grocery store. It is delicious either way!

There are two ways I prefer leg of lamb, too. One is where the outside is crusty and crisp and the interior is rosey pink OR the ultimate where it is exact opposite, fall-off-the-bone tender and smothered in gravy! l roast this about 40 minutes per pound or until the internal temperature registers 175°F. This can take about 5-6 hours or so.

Serve with Roasted Mashed Potatoes for a warm, buttery, creamy addition to your dinner. Some Roasted Vegetables would also make a great side, as would this Wild Rice Pilaf.

overhead shot of seasoned leg of lamb in roasting pand with vegetables and herbs

Ingredient Notes and Substitutions

  • Lamb A protein with a strong, earthy flavor. Your cook time will vary depending on choice of cut and weight.
  • Onion, Celery, and Carrots When roasted with these vegetables, the meat soaks up all of their mildly sweet, earthy flavors. The aroma of all three cooking together is unmatched! Yellow or white onions will both work well in this dish.
  • Orange This fruit also contributes to the dish’s tantalizing aroma, helping to tenderize and add a degree of sweetness.
  • Garlic Have 15 to 20 cloves on standby for this dish. Due to its role in the pan gravy, I would not substitute this ingredient.
  • Rosemary Pairing beautifully with the meat, carrots, and orange, this herb has a complex flavor profile that matches well with citrus, sweet, and peppery notes. Thyme or sage could be used, if necessary.
  • Beef Broth We will roast the meat in a mixture of beef broth and water, helping it to moisten and tenderize. 
  • Flour – Use this to thicken the leftover juice from the roast, creating a mouthwatering pan gravy to serve with our dish.
close up of Slow Roasted Leg of Lamb

How to Make Roast Leg of Lamb

  1. Preheat. Preheat your oven based on the baking instructions for your chosen cut of meat below.
  2. Slice the Vegetables. Cut the onion and orange into quarters. Separate and remove the skins of your garlic. Slice the celery into uneven, large chunks. Add to a pan alongside the carrots and rosemary.
  3. Season the Meat. Sprinkle salt and pepper over the entire surface, pressing and massaging the seasonings into the meat. If using bone-in, lay the cut down with the bone side up. Pour the beef broth and water into the roasting pan. Finally, pour the olive oil over the meat. Cover the pan with a large piece of aluminum foil.

Watch the Video How to oven roast boneless leg of lamb

Want to see the recipe in action from start to finish? Just watch the video below!

How to Cook Boneless VS. Bone-In Leg of Lamb

  1. Boneless: Cook based on the weight of the meat. The netting should be left on to hold the de-boned pieces together. Leave the netting on a boneless cut of lamb until it is fully cooked, then cut it off with a pair of kitchen shears prior to carving. For a 4-7 lb cut, set your oven to 325°F. Adjust roasting times based on desired doneness:
  2. Medium Rare: Cook for 20 minutes per pound, with an internal temperature of 145°F.
  3. Medium: Cook for 25 minutes per pound, with an internal temperature of 160°F.
  4. Well-Done: Cook for 30 minutes per pound, with an internal temperature of 170°F.
  5. Fall off the Bone Tender Lamb: Cook 40 minutes per pound or until the internal temp registers 175°F. This can take about 5-6 hours or so.
  6. Bone-In: Again, adjust based on how many pounds of meat you’re cooking. Set your oven to 300°F.
  7. For a 4 to 4.5 lb cut, cover the pan and cook for 4.5 hours. Remove the cover and roast for 45 minutes longer to achieve a golden brown crust. If the meat is 6 to 6.5 lbs, roast covered for an additional hour.

HOW TO MAKE PAN GRAVY FOR SLOW ROAST LEG OF LAMB

  1. Remove the Veggies. Transfer the pan, with all the juice and vegetables still inside, to your stovetop. Remove the vegetables, rosemary, and orange.
  2. Mash and Boil. Using a masher or wooden spoon, mash the roasted garlic. Mix this with the juices in the pan, then heat the juice until it begins to boil.
  3. Thicken with Flour. In small increments, whisk in the flour until everything is well combined. Then, simmer the gravy over low heat until it thickens. 

Gravy Tip

If your gravy is too thick, add small amounts of water until you have reached your desired consistency. Alternatively, mix in additional flour until it is as thick as you like. If desired, strain the bits of herbs remaining in the mixture.

whisk in a roasting pan of gravy

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Is bone-in or boneless leg of lamb better?

There are plenty of pros and cons for either. Bone-in can be more flavorful but trickier to slice and serve. It also takes longer to cook. Boneless does have a quicker roasting time and is easy to carve, but this cut might be more expensive.

How long does it take to slow roast leg of lamb? 

It depends on weight, but this 5 1/2 lb bone-in leg of lamb took about 5 hours and 45 minutes to slow roast until fall apart tender.

What can I serve with roasted lamb? 

I like to serve this dish with mashed potatoes! Since the vegetables used for roasting will be mushy and overcooked, I recommend roasting a separate batch alone if you wish to enjoy them as a side.

spooning gravy over lamb meat
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close up of tongs pulling tender meat from a roast leg of lamb

Slow Roasted Leg of Lamb (Bone-In or Boneless)

4.74 from 19 votes
Succulent leg of lamb is slow roasted with garlic, citrus and rosemary. Recipe for boneless or bone-in leg of lamb, gravy and how to video.
Servings: 8
Prep: 15 minutes
Cook: 5 hours 30 minutes
Total: 5 hours 45 minutes

Equipment

  • 1 Large Roasting Pam Large Roaster: 16 3/4" x 13 3/4" x 2 1/2" high overall; 5 lb. 6 oz.; holds up to 20-lb. turkey.

Ingredients 

  • 5 1/2 lb leg of lamb (bone in) (For boneless, See Note 1)
  • salt
  • black pepper
  • 1 large onion quartered
  • 1 large orange quartered
  • 2 ribs celery
  • 2 cups cut carrots
  • 1 large head of garlic (about 15-20 cloves)
  • 3-4 fresh rosemary sprigs (6+ inches long)
  • 4 cups beef broth
  • 2 cups water
  • 2 tbsp olive oil
  • 1/4 cup all purpose flour

Instructions 

  • Preheat oven to 300°F for bone-in, 325°F for boneless.
  • Cut and quarter the onion and orange. Break up the head of garlic and remove skins or have 15-20 cloves peeled and ready. Rough chop the celery and set all in the bottom of a large roasting pan with the carrots and rosemary.
  • Lay the leg of lamb on top and season generously with kosher salt and black pepper on both sides. Leave the bone side up and pour in the beef broth and water. Drizzle the olive oil on top of lamb and then cover with aluminum foil and place in the hot oven (See Note 2 for different weights and roasting times).
  • Remove from oven and set aluminum foil aside. Carefully flip leg of lamb, baste with pan juices and return to oven. Roast, uncovered, basting every 15 minutes, for 45 minutes or until the outside is a rich, golden brown.
  • Remove lamb from pan and keep warm on a serving plate with the aluminum foil covering.

For Pan Gravy

  • Move roasting pan to stove top over 2 burners. Using a slotted spoon remove the vegetables (See Note 3), rosemary sprigs and citrus, leaving the roasted garlic. Mash the garlic with the back of a wooden spoon and bring the pan juices to a boil. Sprinkle the flour over the gravy and whisk to incorporate. Turn heat to low and simmer until thickened. Add water if too thick, or cook longer to reduce if gravy is thin. Feel free to strain if you do not want the garlic/rosemary pieces and serve alongside roasted leg of lamb. I serve with mashed potatoes.

Video

Notes

Boneless Leg of Lamb: For 4-7 lb Boneless Leg of Lamb, roast in a 325°F oven roasting times as follows:
  • Medium Rare (internal temp should be 145°F) 20 minutes per pound
  • Medium (internal temp should be 160°F) 25 minutes per pound
  • Well Done (internal temp should be 170°F) 30 minutes per pound
  • Fall off the Bone Tender Lamb: Cook 40 minutes per pound or until the internal temp registers 175°F. This can take about 5-6 hours or so
The netting should be left on to hold the de-boned pieces together. Leave the netting on a boneless cut of lamb until it is fully cooked, then cut it off with a pair of kitchen shears prior to carving.
 
For Bone in Leg of Lamb: For this recipe I use a 5.5 pound leg of lamb that feeds about 6 to 8 people. Oven temperature should be 300°F.
  • 4 to 4.5 pound leg of lamb roast covered for 4.5 hours and uncovered for another 45 minutes or until the outside is a rich, golden brown.
  • 6 to 6.5 pounds, roast covered for 5.5 hours and uncovered for another 45 minutes or until the outside is a rich, golden brown.
  • Fall off the Bone Tender Lamb: Cook 40 minutes per pound or until the internal temp registers 175°F. This can take about 5-6 hours or so. This is what is shown in video.
2. Feel free to eat the roasted vegetables when serving, but I find they can be a little over cooked myself and serve the lamb with mashed potatoes and other steamed or roasted vegetables if desired.

Nutrition

Calories: 339kcal | Carbohydrates: 11g | Protein: 43g | Fat: 12g | Saturated Fat: 3g | Cholesterol: 125mg | Sodium: 606mg | Potassium: 806mg | Fiber: 1g | Sugar: 3g | Vitamin A: 4505IU | Vitamin C: 12.6mg | Calcium: 55mg | Iron: 4.4mg

The information shown is an estimate provided by an online nutrition calculator. It should not be considered a substitute for a professional nutritionist’s advice.

Course: Dinners
Cuisine: American
Have You Made This Recipe? Let Me Know on InstagramTag @keviniscooking or tag me #keviniscooking!
tender leg of lamb with spoon and gravy

Kevin

Whether in the kitchen or on the grill, you’ll find me cooking American favorites with a love for BBQ, Mexican and Tex Mex. I’m passionate about making tasty food because life’s too short to be bland!

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73 Comments

  1. 5 stars
    Once again it was delicious! I made it last year with a 5.5 pound bone-in and came out so tender. Love the orange flavor in the gravy, too.

  2. 3 stars
    I was really excited to try a slow roast recipe wanting a delicious fall apart lamb roast. I used a 5.3Lb boneless leg of lamb and slow roasted it to an internal temp of 175. Then removed the foil, turned and roasted for 45min. (all per instructions). I was expecting a moist pull apart roast but instead it was dry and leathery. Thankfully the gravy was fabulous and it covered up the meat. I would definitely not try this recipe again.

    1. It’s really hard to read that it was dry? It is basically braised in liquid for 4+ hours covered. Sorry that was you experience Susan. Wondering how the temp of your oven is. You did baste as well in last uncovered part?

    1. 3 stars
      Hi! Happy Easter!!! I’m sorry I only gave this 3 stars because I followed the directions exactly and mine came out kind of dry. I always do lamb shanks, I think because I’ve perfected them and going forward, I’ll probably do those next Easter.
      Kevin, when you touch that lamb with your tongs, I drool every time. I wish, so badly, mine would have come out just like yours. Thank you for sharing!

      1. It’s really hard to read that it was dry? It is basically braised in liquid for 4+ hours covered. Sorry that was you experience Jo. Wondering how the temp of your oven is. Was this bone-in or boneless, different cooking and temps for both?

  3. I’ve never cooked lamb before, I’ve heard that it has weird gamey flavor. Do you do anything to get rid of it, or just cook as is? I really want to try this recipe but concerned I may not like it because of that pesky gamey flavor everyone is talking about. I am not really sure what it would taste like

  4. 5 stars
    I am from South Africa and first Christmas in US cooking different Christmas dishes. Have used several of your appetiser, main meal and dessert recipes and they are successful and delicious. Thank you for assisting a new American cook

  5. 5 stars
    Made this like the video, came out fantastic. Talk about fall of the bone good!!! Made the gravy without the braised veg and guests took leftovers. Fantastic and second time making this. Thanks for a dependable recipe everytime Kevin.

    1. 5 stars
      YUM, absolutely delicious and different, I cooked the pull apart method as featured on the video. As Aussies we often eat lamb but have never thought of cooking a leg of lamb in this method.
      My husband said this is the best thing I have ever cooked so this recipe is a keeper.
      Thankyou Kevin for recipies that can be trusted and your attention to detail and presentation is amazing. 😊

      1. I so appreciate you coming back to share this and am happy you’re enjoying the recipes Carol. You made my day! 🙂

  6. 5 stars
    Did the 20 minute per pound, blush pink inside route and wow, just perfect timing! My kind of lamb. Thanks for a new method and recipe!

  7. 5 stars
    So, just cooked this for my regular Guinea Pigs (pigs is appropriate as they eat everything that is good and always willing to try new things I throw at them). And we all LOVED your recipe!

    My only question is, I cooked as instructed (5 1/5 pound leg, bone in, at 300 degrees for 4.5 hours , instead of 5 and then turn – because I wanted to check temp of meat early). When I pulled it out, temp was showing 209-213 throughout the meat. I was hoping to finish it at 145ish and let it rest. The ONLY thing I deviated from the instructions was, instead of a roasting pan, I did use a Dutch oven type pot.

    As stated above, your recipe is absolutely delicious. The meat was moist, tender, and I will definitely add to my list of go to recipes. Only pointing out if you choose to use a Dutch oven, maybe limit the cook time?

    Thank you for your gift!

    1. I’m so happy that you and the “Guinea Pigs” enjoyed this one James! Thanks for coming back to let me know.

    2. We prefer not to use aluminum foil on food while it is cooking so we were going to use a dutch oven instead. We interpreted one of the comments to indicate that using a dutch oven may cook the lamb faster than anticipated. Please advise what temperature to use and for how long when using a dutch oven.
      Thanks for your recipe – we will be using it anyway.

      1. Lillian, if going the Dutch oven route (and I’m assuming boneless), simply use a meat thermometer to the desired temperature you prefer. See the recipe card as well as post for all times and temps. Hope this helps.