In a bowl, mix together the salt, cumin, fennel seeds, ginger, cumin, chilli, coriander, cardamom seeds, olive oil and yoghurt
Place the yoghurt in a large freezer bag and place the lamb inside.
Rub the mixture all over the lamb and let it marinade for at least 3 hours, turning the lamb over a few times
Preheat the oven to 150 degrees C
Place the potatoes and bay leaves in a large roasting tray
Pour the water over the potatoes, place the lamb on top, squeezing any yoghurt out of the bag over the lamb
Cover the tray with foil, sealing all around the edges. Place in the oven and cook for 2 hours and 15 minutes.
Turn the oven up to 210°C and cook uncovered for 30 - 45 minutes, until the lamb and potatoes are crisp
Let the lamb rest for 10-15 minutes
While the lamb rests, mix together the ingredients for the raita (optional)