Preheat the oven to 150c (fan oven) 170c (standard) - ensure that the lamb has rested at room temperature for around an hour

Get the ingredients ready to cook the lamb

Chop the onion and put into the roasting dish

Add the garlic and place the lamb on top of the onion along with the rosemary 

Add the red wine to the roasting tray

Add the olive oil to the lamb and then cover with tin foil

Place in the oven and roast for 4.5 hours

After 4.5 hours, remove the foil from the lamb and check that it is tender. (You can do this by prodding it with a fork). If it is not, return it to the oven with the tin foil on. 

If the lamb is tender, return it to the oven with the tin foil off for a further 40 minutes or until browned. (keep the tin foil - you will need it later)

Once browned, remove from the oven and cover with the juices in the bottom of the pan and once again cover over with the tin foil whilst you finish off the other parts of the roast) The lamb will stay warm for around 30 minutes.