Remove the bone from the lamb and cut the meat into bite size pieces. Place lamb in a container with the yoghurt, garlic, ginger and 1 teaspoon of salt.  Mix until well combined.  Cover with a lid and place into the refrigerator to marinate overnight.  Remove lamb from fridge 30 minutes before cooking.

Place a large Dutch oven over medium heat.  Add oil and onions and cook on medium heat for 15 minutes, stirring occasionally.  Reduce heat to low and add 4 cardamom pods, bay leaves, garam masala, Kashmiri chill and 1 teaspoon ground turmeric.  Sauté for 2 minutes until the spices become fragrant.  Add the marinated lamb with the yoghurt and bone broth.  Stir to combine and increase heat to bring to a simmer.  Once at a simmer, reduce heat to low, cover with lid and simmer for 30 minutes until the lamb is tender.

Wash the rice thoroughly and soak in water for 20 minutes.  Place a small saucepan over low heat and warm the milk until it starts to bubble.  Remove pan from heat and crumble the saffron threads into the milk.  Steep for 10 minutes.

Preheat oven to 180°.  Drain the rice and transfer to a saucepan with ½ teaspoon ground turmeric, lemon juice, 1 teaspoon salt, 4 green cardamom pods and enough water to cover the rice.  Bring to boil and boil rice uncovered for 5 minutes.  Strain the rice, discarding the water.  Place the drained rice back into the saucepan and stir in the saffron infused milk.

Remove the lid from the Dutch oven and stir the lamb.  Transfer the rice to the dutch oven, spreading the rice into an even layer.  Scatter with cashew nuts, raisins, coriander, and mint.  Top with pieces of butter.  Cover the Dutch oven with 2 sheets of tin foil overhanging the edge and cover with lid to form a tight seal.  Place into oven for 20 minutes at 180°C. Remove from oven and stand for 5 minutes.

Serve straight from the Dutch oven or transfer the biryani to a platter.