You should be able to find dried rose petals in Middle Eastern stores or online, but if you can’t, just leave them out. It is nice to finish this dish with fresh rose petals or other edible flowers, but only if they’ve been grown organically or specially for eating.
In a pestle and mortar, bash the garlic and ginger together with the salt until you have a rough paste. Put to one side.
Prepare the spice mix (see overleaf) by placing all the whole spices, except for the cinnamon, in a food processor, spice grinder or pestle and mortar and grind everything to a fine powder. Stir in the turmeric and chilli powder. Put to one side.
Heat some oil in a large, heavy-based pan (with a lid). Season the lamb and brown in the pan until golden on all sides. Remove from the pan and set aside. Add the onions to the pan and stir well, picking up the sticky bits from the bottom of the pan. When the onions begin to soften, stir in the garlic and ginger mix and another dash of oil if necessary, and cook for 2 minutes before adding the spice mix and the cinnamon stick. Continue to cook for another 5 minutes, until the onions are soft and the spices smell wonderful.
Return the lamb to the pan and add the tomatoes, vinegar, yoghurt and ground almonds, stirring to pick up the spices stuck on the bottom of the pan. Taste for seasoning, and add enough cold water to easily cover the lamb. Bring to the boil, put the lid on the pan and leave to simmer for 4 hours, until the lamb is tender.
Preheat the oven to 180°C/350°F/gas 4. Drain the rice and cover with boiling water and a pinch of salt. Boil for 4 minutes, then drain and leave to steam in its pan with a lid.
Generously cover the bottom of a large, ovenproof dish with half the lamb mixture. Cover with half the rice, then the remaining lamb and, finally, the remaining rice. Pour in the saffron water.
Place the flour in a large bowl, and work in enough cold water to make a stiff dough. Knead until you have a smooth dough, then roll out with a floured rolling pin, and use to cover the dish. Pinch the sides to make sure it stays tight. Bake for 20–25 minutes, until the bread dough has turned golden.
Serve the biryani with the bread crust intact for your guests to break into. Arrange the rose petals, coriander leaves and pomegranate seeds on the side to sprinkle over the rice.