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. So sorry for the late reply as I have been away on a much needed vacation outside the USA. Needless to say, about your comment…Yes you cover it as stated in Step 3 Lisa “Drizzle the olive oil on top of lamb and then cover with aluminum foil and place in the hot oven for 5 hours (See Note 2 for different weights and roasting times).” Hope this helps!

  1. 4 stars
    Made this last night. It was delicious – more like a pot roast the extra cooking took a lot of the strong lamb flavor away. I did take it out early because it was already at shredding stage. I missed the step to flip it over so it was a little dry on one side but the gravy fixed that. Orange was a nice touch. Didn’t overwhelm. Thanks for the recipe.

  2. 5 stars
    Hi Kevin,
    This recipe looks amazing! I have a small boneless lamb roast – 4.25 lbs. I would prefer to slow roast it to the tender, fall-apart stage. Is that even possible with a boneless roast?

  3. 5 stars
    Yes made this last night for the family and we all enjoyed it. Initially I thought there was too much stock left in the pan but worked out perfectly for the gravy. I think I should have taken it out of the oven a little bit earlier but it was tender. My carrotts were not mushy at all and I enjoyed them with my side of mash. Thanks for the recipe.

  4. Hi Kevin, as my oven is fan forced do I need to change the length of cooking time? Making this today for my son’s family. Will let you know how it goes.

    1. Not the length of cooking time, but drop the temp by 25 degrees. That should do it if using a convection oven (fan forced air). Let me know how it turns out Mary!

  5. are your oven temperatures for fan assist? If not, I assume I should drop the temperature? Thanks. Can’t wait to try this out!