Barbecue roasting butterflied lamb legs and shoulders

Barbecue roasting a butterflied lamb shoulder or leg in a covered barbecue is a fast way to cook a lamb roast using ‘indirect cooking’. Ask your butcher to bone and butterfly the lamb shoulder or leg for you.

Guide to barbecue roasting a boned, butterflied lamb leg or butterflied lamb shoulder.

  1. Preheat the barbecue to 200ºC (the burners should be set at medium). Determine the weight of the lamb (once the bone has been removed) and brush it lightly with oil. Season with salt, pepper and flavourings.
  2. Place the beef or lamb in the centre of the barbecue. Turn the burners directly under the meat off. The remaining burners are left on to conduct and circulate the heat around the roast.
  3. Close the lid and roast for the recommended cooking time:
    • Rare: 20-25 mins per 500g
    • Medium: 25-30 mins per 500g
    • Well done: 30-35 mins per 500g

For ease and accuracy use a meat thermometer.

  1. Remove roast when cooked to desired degree. Transfer to a plate, cover loosely with foil and rest for 10-20 minutes before carving. Carve the roast across the grain to ensure tenderness.

You’ll find a butterflied lamb shoulder or leg has an uneven thickness, so the thinner parts will cook faster than the thicker parts, which naturally means some will be cooked a little more, some a little less.

Cooking to no more than a medium doneness will keep all of the meat juicy and not overcooked.

Preheating a kettle barbecue

If you are cooking your roast in a kettle barbecue, preheat according to the cooking guide that came with your barbecue. As a general rule, heap about 25 heat beads in rails on each side of the barbecue. Light the beads and allow them to develop to a fine, white ash stage (this takes about 30 minutes).

Tips for cooking a roast in a barbecue

  • If you have enough time, take the lamb from the fridge about 15 minutes before cooking.
  • If you are using a charcoal barbecue, light it 40 minutes before you want to start cooking.
  • If you are using a gas barbecue, light it 10 minutes beforehand.
  • Place the lamb in the centre of the barbecue, with the skin side up.
  • Make sure there is no direct heat under the lamb. Burners directly under the lamb should be off, or coals pushed to the side.
  • Cook the lamb once only on each side, turning it too often will toughen the meat. Lower the heat if it is cooking too quickly. 
  • Avoid lifting the barbecue lid too often (you lose about 10ºC to 15°C each time).
    • To boost the temperature in a kettle barbecue during roasting, add 6 to 10 heat beads on each side at 1 hour intervals.
    • Avoid ramping up the flame directly under the meat when adjusting the heat as this dries the roast out (giving it a tough under-side).
  • Check if it’s ready just before the estimated cooking time is up as the meat will continue to cook once it has been removed form the barbecue and is resting.
  • Use tongs to test the roast’s doneness. Gently prod or squeeze the roast, rare is soft when pressed, medium is springy and well done is very firm. For more information on doneness go to How to tell when meat is ready or 'done'.
  • Give the lamb time to rest after cooking. This gives the juices in the meat a chance to redistribute, giving a deliciously moist and tender result.  Cover the roast loosely with foil and rest it for 10-15 minutes before carving.

Love garlic?

Here’s how to flavour a butterflied lamb with your favourite ingredient:

Peel two or three cloves of garlic and cover them with boiling water for a few minutes. Drain and then cut the garlic into thin pieces. This takes any raw flavour from the garlic, particularly if you like your lamb cooked to medium or medium rare. Make small incisions over the top of the lamb and push the garlic in.

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