Step 1

Preheat the oven to 200ºC/400ºF/gas

Step 2

Light the barbecue and prepare a hot side and a cooler side.Halve the lemongrass lengthways, and peel and roughly chop the ginger and garlic, then bash in a large pestle and mortar with the lime leaves.Add the cumin, finely grate in the zest from 1 lemon, and squeeze in its juice. Mix well.Season the lamb with sea salt and black pepper, then rub the marinade all over and leave to marinate for at least 1 hour, preferably overnight.Place the lamb in a snug-fitting roasting tray, cover tightly with a double layer of tin foil, then roast for 40 minutes if you like your meat pink, or slightly longer if you prefer it more well done.Transfer the lamb to the hot side of the barbecue for 10 to 15 minutes, or until you have a lovely smoky, crispy surface – it will sizzle and there might even be a few flames, but move it around to stop it burning. Remove to a board to rest.Meanwhile, pick, finely chop and place the mint leaves in a bowl, add a few good dollops of yoghurt and a good squeeze of lemon juice, then mix together and season to perfection.Slice up the lamb, then serve with the minty yoghurt and wedges of lemon for squeezing over. Delicious served with a seasonal salad.