Slow roast Leg of Lamb : Tender, Juicy & Packed with Flavour

Slow roast leg of lamb is the dish I make whenever the whole family is coming round: Christmas, Easter, Eid or just a big Sunday lunch. Three hours in the oven turns the meat so tender and juicy that it practically falls off the bone.

It’s an easy recipe because the oven does nearly all the work. Below you’ll find my 3-hour method, plus 4-hour and 7-hour versions, a cooking time chart by weight, fan oven and gas mark settings, and a quicker pink roast for when you’re short on time.

Why you’ll love this slow roast lamb

• Meltingly tender meat, no thermometer or guesswork needed.
• Just 20 minutes of prep, then the oven takes over.
• You pick the timing that suits your day: 3, 4 or 7 hours.
• The onions and pan juices make a gorgeous gravy with no extra effort.
• It feeds a crowd and is very forgiving if lunch runs late.

How much lamb per person?

Allow 200–250 g of boneless meat per person, which works out at roughly 300–350 g of bone-in leg each.

Number of people	Bone-in leg of lamb
4	1.2–1.5 kg
6	1.8–2 kg
8	2.5 kg
10	3 kg

For this recipe I used a 1.2 kg leg. There were six of us at the table, two adults and four children aged 5 to 15, and we still had leftovers. If everyone’s a hearty eater, the same leg will comfortably feed four adults.

Ingredients for a tender roast leg of lamb (1.2–1.5 kg)

• 1 bone-in leg of lamb, 1.2–1.5 kg
• 6 garlic cloves
• 2 sprigs of fresh rosemary
• 30 g butter
• 3 tbsp olive oil
• 2 onions
• 2 bay leaves and a few sprigs of thyme
• ½ tsp ground coriander (optional, but it’s how I’ve always done it)
• sea salt and freshly ground black pepper
• 250 ml vegetable or lamb stock (or water)

You can add carrots or celery under the joint with the onions. They flavour the juices and lift the meat off the bottom of the tin.

How to slow roast a leg of lamb: 3, 4 or 7 hours

The longer you cook it, the lower the oven goes. Whichever timing you choose, the lamb is cooked right through until it’s completely tender, so it isn’t served pink.

Time	Conventional oven	Fan oven	Gas mark	Covered?	Result
3 hours	180°C (350°F)	160°C	4	Uncovered, foil at the end if needed	Tender, slices thinly
4 hours	160°C (325°F)	145°C	3	Foil for the first 3 hours	Very tender
7 hours	120°C (250°F)	110°C	½	Covered throughout (casserole or foil)	Pulls apart with a fork

For all three, I start with 15 minutes at 220°C (200°C fan, gas 7) to brown the outside and build flavour, then turn the oven down. This two-stage method, hot then low, is the secret to a golden crust with soft meat inside.

3-hour slow roast leg of lamb (my go-to)

This is the version I make most often. The meat is tender and juicy but still holds together, so you get proper slices for the table. The full method is below.

4-hour slow roast leg of lamb in foil

After the first 15 minutes at 220°C, turn the oven down to 160°C (145°C fan, gas 3). Cover the tin with foil, crimping it tightly round the edges to trap the steam. Take the foil off for the last hour so the lamb can brown, and baste every 30 minutes.

7-hour leg of lamb

After browning, turn the oven down to 120°C (110°C fan, gas ½). Pour 400 ml of stock into the tin and cover tightly. Baste every hour. For the last 30 minutes, uncover and turn the oven up to 200°C to colour the top. The meat falls apart on its own, so you serve it with a spoon rather than a carving knife.

Pot-roasting in a casserole dish

Any of these methods works in a lidded cast-iron casserole that goes in the oven. Keep the lid on so the lamb braises in its own steam, then take it off for the final 30 minutes to give it some colour.

Fan oven or conventional?

Both work well. In a fan oven, just drop the temperature by 15–20°C, as shown in the table. Fan ovens dry meat out a little more, so baste generously and keep a tray of water in the oven.

Leg of lamb cooking times by weight

Weight (bone-in)	Slow roast at 180°C (160°C fan)	Quick roast, medium, at 180°C
1 kg	2 hr 45 min	40–45 min
1.2–1.5 kg	3 hours	50–60 min
2 kg	3 hr 30 min	1 hr 15–1 hr 20
2.5 kg	4 hours	1 hr 35–1 hr 40
3 kg	4 hr 30 min	1 hr 55–2 hours

For a quick roast, take off 10 minutes for pink lamb, or add 10 minutes per kilo for well done. These times include the initial browning but not the resting time.

Boneless leg of lamb? A boned and rolled joint cooks a little faster. Knock about 10 minutes per kilo off the times above and check it 20 minutes early.

Step-by-step: slow roast leg of lamb

1. Take the lamb out of the fridge at least 30 minutes before cooking.
2. Heat the oven to 220°C (200°C fan, gas 7). Put a shelf low down and take out the ones above it, so you don’t burn your hands every time you baste (I’ve done that more times than I’d like to admit!).
3. Pat the lamb dry with kitchen paper, then rub it all over with olive oil.
4. Using a small, sharp knife, make little cuts all over the fatty side. Push a sliver of garlic, a small sprig of rosemary and a knob of butter into each one.
5. Season generously with salt and pepper, and sprinkle over the coriander if using.
6. Scatter the sliced onions, bay and thyme over the base of a roasting tin. Drizzle with a little oil and pour in the stock. Sit the lamb on top, fat side up.
7. Put a tray of water on the top shelf. Roasting in a steamy oven is what keeps the meat juicy.
8. Roast for 15 minutes, then turn the oven down to 180°C (160°C fan, gas 4) and cook for 3 hours.
9. Every 30 minutes, turn the lamb and baste it with the juices. If the tin looks dry, add half a glass of water, and top up the water tray too.
10. If the lamb is getting too dark, cover it loosely with foil for the last 30 minutes.
11. Lift it out of the oven, tent it loosely with foil and leave it to rest for 30 minutes before carving.

How do you know when it’s done?

For slow-roast lamb, the fork test is all you need: a fork should slide in with no resistance, and the meat should come away from the bone easily. By then it will be well above 80°C in the middle.

For a quick roast, a meat thermometer pushed into the thickest part (not touching the bone) is the most reliable guide:

• 55–58°C: pink
• 60–63°C: medium
• 70°C and above: well done

No thermometer? Pierce the meat: red juices mean it needs longer, rosy juices mean medium, and clear juices mean well done. Try not to prod it too often, or you’ll lose those precious juices.

How long should lamb rest?

Rest a slow-roast leg for 30 minutes, loosely covered with foil. It stays hot for a good 45 minutes, which gives you plenty of time to make the gravy and finish the sides. A quick-roast leg needs 10–15 minutes.

Easy gravy from the pan juices

While the lamb rests, tip the roasting tin slightly and spoon off most of the fat. Mash the soft onions into the juices, add a splash of stock or water and scrape up all the sticky bits from the bottom. Simmer for a couple of minutes on the hob, season to taste, and you have a rich onion gravy with no flour needed.

How to carve a leg of lamb

Hold the shank (the narrow bone end) with a cloth or carving fork. Cut slices across the grain, working down towards the bone, then turn the joint and carve the other side. After a 7-hour roast, skip the knife and simply pull the meat apart with two forks.

Quick roast: pink leg of lamb in under an hour

No time for a slow roast? Prepare the lamb exactly the same way (garlic, rosemary, oil, onions), then roast it at 180°C. For a 1.2 kg leg, allow 40–45 minutes for pink, 50–55 minutes for medium and 60–65 minutes for well done. Baste it two or three times, then rest it under foil for 10–15 minutes.

The meat will be firmer and pinker, rather than melt-in-the-mouth. You can also watch my quick roast leg of lamb video.

Why is my roast lamb tough?

With a quick roast, it’s usually overcooked: once the middle goes past 70°C, the meat dries out. With a slow roast, it’s usually the opposite. It simply hasn’t had long enough, as the fibres only really relax after about 3 hours. Give it another 30 minutes, covered, and it will turn tender.

How to thaw a frozen leg of lamb

Always defrost lamb in the fridge, still in its packaging and sitting on a tray. Allow about 7 hours per 500 g:

• 1.2 kg leg: about 17 hours
• 2 kg leg: about 28 hours
• 2.5 kg leg: about 35 hours

Once thawed, it will keep for another day in the fridge. Take it out 30 minutes before cooking.

Can you prepare a leg of lamb the day before?

Yes. Stud it with garlic and rosemary, season it the night before, then cover and keep it in the fridge. Slow-roast lamb also reheats beautifully: cover it with its juices and warm it through at 160°C for 20–25 minutes. Leftovers keep for 3 days in the fridge and are brilliant in sandwiches or wraps.

What to serve with roast leg of lamb

• creamy mashed potatoes, with the onion gravy spooned over
• crispy roast potatoes
• roasted carrots, parsnips and shallots
• green beans, peas or flageolet beans
• celeriac or parsnip mash

For sauces, the pan gravy is often all you need. If you like the British classics, mint sauce or redcurrant jelly are lovely with lamb. A peppercorn sauce or a fresh chimichurri also work really well.

FAQs: slow roast leg of lamb

Should you cover lamb when roasting?

For the 3-hour method, no: only cover it at the end if it’s browning too fast. For 4 hours, cover it for the first 3 hours. For 7 hours, keep it covered until the last 30 minutes.

What temperature do you slow roast lamb at in a fan oven?

160°C fan for 3 hours, 145°C fan for 4 hours, or 110°C fan for 7 hours, after an initial 15 minutes at 200°C fan.

How long do you cook a 2 kg leg of lamb?

About 3 hours 30 minutes as a slow roast at 180°C, or 1 hour 15–20 minutes for medium as a quick roast.

How long does a 1.2 kg leg of lamb take?

3 hours as a slow roast at 180°C (160°C fan), or 50–55 minutes for medium as a quick roast.

Do you need to sear the lamb in a pan first?

No. The first 15 minutes at 220°C give it all the colour it needs.

More roasts to try

• Slow oven-braised lamb shanks
• Roast stuffed turkey
• Juicy oven-roasted chicken
• Oven-baked clementine glazed salmon