Heat oil, and fry the onions with the bouquet garni until golden brown. Add the spices and cook for a few mins. Add the ginger and garlic paste and continue to cook for a few mins. Sear the lamb shanks in a hot pan until golden and season with salt and pepper. Add the shanks to the pot with spices, followed by the water to just cover the shank. Wrap the pot with foil and braise in the oven at 140C for 2 hrs.
Mix the crust ingredients together to make the dough. Set aside for 20 mins, and roll out the dough to a little larger than the dish it will be served in. Make a hole in the centre of the dough – the same width of the lamb shank bone – and set aside.
To make the biryani, heat ghee in a pot, add the onions and fry until golden brown. Add all the spice powders, except the garam masala and cook for a few minutes. Add the ginger and garlic paste, and continue to cook for a few mins. Place the lamb cubes in the mixture and brown off in the pan. Cover with water and simmer until the lamb cubes are tender.
Boil the rice with the bouquet garni until the rice is almost cooked, then strain. Put the rice on the meat and add the saffron water, cream, mint, coriander, kewra and rose water. Cover the pot and cook on a low flame for 5 mins.
Place the biryani in an oven proof dish and make a well in the centre to place the cooked lamb shanks. Pack the biryani around the lamb shank and cover the lamb bone with foil. Wrap the rolled out crust over the lamb shank – make sure the bone pops out through the hole in the centre – and seal the crust around the dish, brush with clarified butter and bake in the oven for 6 mins before serving.