Directions:

Mix the ingredients (2-7) together to make the marination

Make small incisions all over the lamb, then insert the 5 garlic pieces into the incisions

Break off little pieces of rosemary and "spike" these into the remaining holes

Rub the lamb with the marinade and leave minimum 6 hours in the fridge (preferable overnight)

Sit the lamb on a wire rack in a roasting tray and leave at room temperature for about 1 hour before roasting, so it will cook evenly

Preheat the oven to 200°C, fan 180°C, gas 6

Put the onions, carrots and celery into the bottom of the roasting tray (under the lamb on its rack) with the rest of the marination and a few rosemary sprigs

Brown the lamb in the oven for 15 minutes, then turn the temperature down to 180°C, fan 160°C, gas 4

Roast for a further 2 hours or depending on how you like your lamb cooked

Remove the lamb from the over and leave to rest for 20 minutes

To make the gravy: Pass the vegetables and juice from the roasting tray through a sieve

Add the chicken stock, bring to a simmer, and season

Mix the cornflour with a little cold water, then whisk into the gravy and add any resting juices from the lamb

Simmer till reduced with perfect consistency

Keep warm until you are ready to serve