Slow-Roasted Leg of Lamb with Rosemary and Garlic

Slow-roasted leg of lamb sits firmly in the tradition of a British roast dinner: a generous joint seasoned simply, cooked until tender, then served with potatoes and a proper pan gravy. Rosemary, garlic, Dijon mustard and olive oil form a savoury crust that suits lamb’s natural richness, while the long, gentle roast gives the meat a soft, pull-apart texture rather than a pink, quick-roasted finish. Crisp-edged potatoes make practical use of the oven time, and the red wine and lamb stock gravy draws flavour from the browned roasting pan. It is a straightforward centrepiece for Sunday lunch, Easter, or any meal where deeply savoury roast meat and good gravy are the point.
Cuisine style British Sunday roast-style
Flavor profile Herby • Savoury • Rich
Techniques Slow-roasting • Deglazing • Resting
Key equipment Roasting pan • Meat thermometer
Cooking style Hands-off cooking • Crowd-friendly
Time commitment Slow-cooked

Why this recipe works

  • Gentle slow roasting: Cooking the lamb slowly helps the meat become tender enough to carve or pull apart without drying out.
  • Classic savoury depth: Rosemary, garlic, Dijon and olive oil season the lamb directly, while the browned pan juices build a fuller gravy.
  • Complete roast dinner feel: Crisp potatoes, rich lamb and glossy gravy create the familiar balance of texture and flavour expected from a traditional roast.

Get the most out of this recipe

Timing notes

  • Rest before carving: Allow the lamb to rest for 15 to 20 minutes so it carves or pulls more cleanly and stays moist.
  • Serve the potatoes promptly: The potatoes are best while their edges are crisp; keep them in the switched-off oven only briefly while the gravy reduces.
  • Mostly hands-off: The active work is front-loaded, leaving the long roast time free for preparing the potatoes and finishing the gravy.

Texture tips

  • For pull-apart lamb: Aim for about 90°C (195°F) and check that a knife slides in easily; tenderness is the key sign here.
  • For crisp potatoes: Cut the potatoes into large chunks and turn them once during the hotter stage so the edges brown without breaking up.
  • Avoid soggy potatoes: Roast the potatoes on a separate tray if the lamb pan is crowded or very juicy, then serve the gravy at the table.

Ingredient notes

  • Choose bone-in lamb: A bone-in leg suits slow roasting because it holds its shape well and gives the pan juices a deeper savoury character.
  • Use fresh woody herbs: Fresh rosemary gives the rub its clean, resinous flavour; thyme is a softer alternative if you want a gentler herb note.
  • Wine for deglazing: Use a red wine you would drink rather than a harsh cooking wine, as the flavour concentrates while the gravy reduces.

Make-ahead tips

  • Store leftovers safely: Cool leftovers quickly, then refrigerate in a sealed container for up to 3 days.
  • Freeze with gravy: Freeze sliced lamb with a little gravy to help protect it from drying out, then defrost overnight in the fridge.
  • Reheat covered: Warm leftovers covered at 180°C (355°F) until piping hot, adding gravy to help keep the meat moist.

Equipment you'll need

Ingredients
Instructions
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  1. Heat the oven to 160°C (320°F). Pat the lamb dry and place it in a roasting pan.
  2. Strip the rosemary leaves and finely chop them, then finely chop the garlic. Mix the rosemary and garlic with 2 tbsp olive oil, the Dijon mustard, 1 tsp fine sea salt and the black pepper to make a paste.
  3. Rub the paste all over the lamb, working it into any natural seams. Roast for 2 hours, basting once halfway through if you like, until the lamb is very tender and a thermometer reads about 90°C (195°F) for pull-apart texture.
  4. Meanwhile, peel the potatoes and cut into large chunks. Toss with the remaining 2 tbsp olive oil and the remaining 1 tsp fine sea salt.
  5. After the lamb has had 2 hours, increase the oven to 220°C (430°F). Add the potatoes to the oven (on a separate tray if you have one, or around the lamb if there is space) and roast for 45 to 55 minutes, turning once, until deeply golden and crisp at the edges.
  6. Transfer the lamb to a board and rest for 15 to 20 minutes, loosely covered. Keep the potatoes warm in the switched-off oven.
  7. Carefully pour off most of the fat from the roasting pan, leaving the browned bits behind. Place the pan over a medium heat, add the red wine and simmer for 2 to 3 minutes, scraping up the sticky bits.
  8. Add the lamb stock and simmer for 8 to 10 minutes until slightly reduced and glossy. Taste and adjust with a pinch more fine sea salt if needed, then carve or pull the lamb and serve with the roast potatoes and gravy.

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Recipe notes

Tips

  • For the most tender result, aim for a slow roast until the lamb is easily pierced with a knife and the internal temperature is around 90°C (195°F), then rest it well before carving.
  • If serving vulnerable groups, make sure the lamb is cooked thoroughly and the gravy is simmered until piping hot.

Substitutions

  • Replace Dijon mustard with whole-grain mustard for a coarser, more rustic crust.
  • Replace fresh rosemary with fresh thyme for a softer, more floral herb note.

Storage

  • Refrigerate up to 3 days
  • Cool leftovers quickly, then refrigerate in a sealed container. Freeze sliced lamb with a little gravy for best moisture; defrost overnight in the fridge and reheat in a 180°C (355°F) oven, covered, until piping hot.

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Slow-Roasted Leg of Lamb with Rosemary and Garlic
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Recipe overview

  • Servings: 4 servings
  • Total time: 3h 45min (25min active)
  • Difficulty: Easy
  • Cuisine: British
  • Allergens:
    Mustard
Beginner friendly Freezer friendly Kid friendly

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