Roasting a leg of lamb is a dream. There will be different sizes of leg available throughout the year, so you're going to have to tell your butcher how many you're cooking for and ask his advice. You're going to want about 300g per person on the bone.
Serves 4-6
1 x approximately 2kg leg of lamb
1 x 2 medium onions
2 carrots
2 sticks of celery
1 bulb of garlic
Olive oil
Sea salt and freshly ground black pepper
Small bunch of fresh thyme, rosemary, bay or sage, or a mixture
Take your lamb out of the fridge 30 minutes before it goes into the oven. Preheat the oven to 240C / 475F / gas 9. There's no need to peel the vegetables - just give them a wash and roughly chop them. Break the garlic bulb into cloves, leaving them unpeeled. Pile all the veg, garlic and herbs into the middle of a large roasting tray and drizzle with olive oil. Drizzle the lamb with olive oil and season well with salt and pepper, rubbing it all over the meat. Place the lamb on top of the vegetables.
Place the roasting tray in the preheated oven. Turn the heat down immediately to 200C / 400F / gas 6 and cook for 1 hour and 30 minutes for blushing pink meat. If you're doing roast potatoes and veggies, this is the time to crack on with them - get them into the oven for the last hour of cooking. Baste the lamb halfway through cooking, and if the veg look dry, add a splash of water to the tray to stop them burning. When cooked to your liking, take the tray out of the oven and transfer the lamb to a board to rest. Cover it with a layer of tinfoil and a teatowel and put aside while you make your gravy and mint sauce.
With lamb I don't think there's a right way or a wrong way when it comes to carving. Wrap a clean tea towel around the end of the bone and hold it firmly. Use a sharp knife to carve the lamb - away from you - in nine slices so you get a good cross-section of meat. When you get down to the bones, just rotate the leg and start carving again. Lay all the carved meat on a serving platter and serve with your piping hot gravy, your mint sauce and your roast veg.