Place the lamb leg in a dish and marinade with salt, ginger paste, garlic paste, rose petals, kasuri methi, Kashimiri chilli powder and green chilli paste. Leave in the fridge for 24 hours.
Cooking the lamb:
Get the lamb out the fridge and rest for 30 minutes to get to room temperature. Place the lamb in a casserole dish and add bay leaves, green cardamom, black cardamom, cinnamon, black peppercorns and pour enough water to cover ¼ of the lamb leg. Cover with the lid and roast for 4 hours, turning the leg every hour, and topping the water if the level goes below ¼.
Once cooked, remove the lamb from the oven and rest for 30 minutes.
Strain the cooking liquid form the casserole dish, discard residue, and add 100ml double cream. Bring to a boil.
Pull the meat from the lamb leg, keeping the bone on the side. Shred the meat with a fork. Add the sauce to the shredded meat, pour melted butter and garam masala. Pile the meat over the bone and place under a hot grill for 5 mins, until the top is crispy.