Ask your butcher to butterfly-bone the lamb for you. Some supermarkets will also do this, including M&S where ordering for parties is available. You can prepare and marinate lamb the day before, then cover and chill until ready to cook.
1 leg of lamb, approx 2.25kg (5lb) weight, butterfly-boned
For the marinade
2tbsp chopped fresh rosemary
2tbsp chopped fresh thyme
Zest of 2 lemons
6 garlic cloves, crushed
130ml (4½fl oz) olive oil
3 fresh bay leaves
Combine marinade ingredients, but don’t add any salt as it draws the juices out of the meat and will toughen it. Make slashes about 2.5cm (1in) deep through the fleshy side of the lamb, but don’t go right through the skin.
Put the lamb skin-side down in a non-metallic dish, pour over the marinade and rub in well. Do this the day before to allow the flavours to penetrate the meat. Cover and chill.
When you’re ready to cook the lamb, preheat oven to 200 C, 180 C fan oven, gas 6.
Place lamb in a roasting tin and season both sides well. Cook in the oven for 45 minutes if you like your lamb blushing pink, or 1 hour if you prefer it more well done.
Remove the lamb from the oven and allow it to rest for 15 minutes.
Pour all juices from the tin into a small saucepan and skim off any fat. Keep hot while you slice the lamb and serve the sauce separately.