Put the lamb into a large saucepan with the water. Bring to the boil and simmer for 5 mins, skimming off and scum or fat as it appears. Add the onion, garlic, celery, saffron, cinnamon, tumeric, ginger, nutmeg, salt and pepper as well as half the chopped coriander. Cook for half an hour before adding the lentils and chana dahl, then simmer for another half hour. Take out the meat and remove from the bone. Return the meat to the pot, along with the tomato paste, flour mixture and lemon juice. check the seasoning stir in the butter and extra coriander.