(This can be done on a  barbecue or works just as well in the oven following the same heat pattern)

50g butter, melted
3 tbsp olive oil
2 tsp ground cumin
2 tsp coriander
2 tsp  paprika
1 tbsp thyme leaves
3 garlic cloves, crushed
zest and juice 1 lemon
1 tsp harissa
2½ kg leg of lamb, butterflied

For the sauce
1 tsp harissa
handful fresh coriander leaves, roughly chopped
300g Greek yogurt

1. Mix the butter and oil in a bowl
2. Stir in the spices, thyme, garlic, lemon zest and juice.
3.  Add the harissa, 1 tsp salt and plenty of freshly ground black pepper
4.  Mix well.
5.  Put the butterflied lamb in a large shallow dish
6.  Spoon over the marinade.
7.  Using your hands, rub it all over the meat.
8.  Cover loosely with foil or cling film
9.  Leave to marinate for at least 2 hrs, or overnight in the fridge.
10.  Light the barbecue, adding plenty of coals.
11.  When it is ready, add the lamb, fat-side down, and cook on a fairly high heat for 5 mins until well browned.
12.  Turn over and cook for another 5 mins to brown the other side.
13.  Move the coals to the sides of the barbecue to reduce the heat under the meat and cook more gently for 30-40 mins, turning occasionally. This timing will give you pink meat.
14.  Remove the meat to a large board and cover tightly with foil. Leave to rest for 10-15 mins.
15.  For the sauce, fold the harissa, a little salt and the coriander into the yogurt.
16.  Cut the lamb into thick slices
17.  Serve with the sauce and couscous or as part of a feast.