In a big stock pot, add onions, wholes spices and lamb pieces with bones. Add a litre of water and bring it to boil. Simmer the heat and cook it for about an hour. You can use the stock immediately or if you have time, as Maunika has mentioned. Let it rest in the pot overnight and it will amazingly enhance the flavors.
Discard the onion and whole spices. Reserve the stock and meat.
Soak the rice for 30 minutes, Use a heavy bottom pan or cast iron pan. Add butter/ oil, when hot, add the bay leaves, cinnamon and cardamom pods and fry them for a few seconds until they realise the aroma.
Add sliced onions and fry the over a medium heat until they are soften and light golden brown. Add ginger and garlic pastes along with green chilles and add rest of the spices ( nutmeg and cinnamon). Cook them for couple of minutes
Mix in cooked lamb and rice.. Season it with salt and add 3 cups of reserved stock. Cover and cook on a low heat for about 20 minutes or until the rice is completely cooked and liquid is absorbed.
Remove from fire and serve it with raita.