mix the marinade ingredients together and rub into the lamb chunks, chill for 2 hours or overnight.
allow lamb to get to room temperature then thread onto wooden skewers.
make a paste of the chillies and nuts in a blender then fry in a little oil gently for 5 minutes.
add the mushrooms, garlic, ginger, yoghurt, garam masala and seasoning. Fry gently for 5 minutes.
in a separate pan fry the rice in a little vegetable oil for about 3 minutes Add just enough water to cover, season with salt and pepper and add the turmeric and cook until tender, about 30 minutes lay out on a tray to dry a little.
Meanwhile, preheat oven to 350F, fry the onion until golden and crisp.
grease either individual ovenproof dishes or one large one with butter and sit the bay leaves on the bottom. Now layer up the rice, mushroom mix, onion and a splash of the lime juice and rosewater.
repeat and then pour over the saffron rice. cover with aluminum foil and cook in the oven for 30 minutes.
When the biryani is done, grill the lamb for about 4 mins, turning regularly and basting with melted butter mixed with the lemon juice.
serve the lamb resting on the rice sprinkled with the mint and drizzled with curry sauce if liked ( ready bought good curry sauce is ideal).