1. Place the lamb in a roasting tin, fat side up. Using a small sharp knife, make deep incisions every 6cm (2½ in) or so all over the top.
2. Next, place a dry frying pan on the heat and tip in the coriander seeds. Allow to get slightly darker in colour and toasted – between 30 seconds and 1 minute then tip into a mortar and grind with a pestle.
3. Place in a bowl and mix in the oil, garlic and chopped coriander, then season with salt and pepper. It should make a lovely thick paste. Rub the paste all over both sides of the lamb and set in the fridge to marinate for at least 1 hour or overnight.
4. When ready to cook, preheat the oven to 200ºC (400ºF), gas mark 4.
Roast the lamb for 30–50 minutes, depending on how you like it cooked. (This is equally good cooked on a barbecue.)
5. Rest the meat for 15–20 minutes after cooking, then carve into slices to serve, not forgetting to drizzle the delicious juices over the lamb.