Preheat the oven 250C/480F.

Place the most of the rosemary (reserve a couple of sprigs), thyme, bay leave, 3 of the garlic head halves and the red onion in the bottom of a high sided roasting dish. Drizzle with the olive oil and season with salt and pepper.

Place the lamb on top of the vegetables and herbs.

Prepare the lamb by slashing through any fat if there is, but not penetrating the meat.

Smear the harissa paste over the meat and sprinkle over the cumin and smoked paprika, season with salt and pepper.

Break up the remaining half head of garlic and bruise the cloves. Place them on top of the meat along with the remaining sprigs of rosemary

Tightly seal the whole tray with heavy-duty aluminium foil ensuring it is completely sealed.

Place in the hot oven and cook for 10 minutes and then reduce the temperature to 180C and leave it to roast for 4 hours. Do not open and check the meat. Just leave it.

After 4 hours take out the oven and remove the lamb and set it aside covered in the foil for about 10 – 15 minutes.

Strain the pan juice and the roast garlic and herbs through a fine sieve into a wide vessel. Press down to release as much liquid as possible. Allow the fat and juices to settle/ separate into distinct layers.

Either use a fat separator to skim the fat off the top, alternatively, lay a sheet of paper towel over the top surface and lift it off with the fat. Repeat this another 4 – 5 more times until no more fat comes off and the towel starts soaking the pan juices.

Carve the meat, it falls off the bone. Shred the meat into large chunks. Reheat the pan juices in a microwave or on the stove top and pour this over the meat.