Put lamb bones to boil in 5 cups water with cinnamon or bay leaf and garlic clove for 30 minutes. Skim off the scum. Strain and set aside.
Wash both dals and soak them separately for 4 hours. Soak the tamarind in 1 cup water for 1 hour, then press out the juice, strain and set aside the tamarind water.
Put both dals into a cooking pot with 8 cups water and 1 teaspoon salt, tumeric powder, 3 green chilis, 1 tablespoon coriander and 10 curry leaves. Cook for 1 1/2 hours or until tender. Liquidize to creamy consistency.
Heat half the oil in another large cooking pot and saute onions for 5 to 7 minutes. Then add the cloves, cardamoms and cinnamon, let cook 2 to 3 minutes, then add the powdered garam masala. Add remaining green chilis, red chili powder, the remaining coriander, 10 curry leaves, garlic puree and ginger puree. Stir to prevent the spices from sticking to the pot. Sprinkle over 2 tablespoons water if necessary.
Add the mutton and saute over a moderate heat for 5 minutes. Add tomato and saute for 5 minutes. Stir in the pureed dals and the stock, adding water to total 4 cups. Add salt to taste and leave to cook, covered, over a moderate heat until the lamb is tender, about 45 to 50 minutes. Then add the tamarind water and remaining curry leaves and simmer for 3 to 4 minutes.
Just before serving, season by heating the remaining 4 tablespoons oil in a small frying pan and fry red chilis, garlic, cumin seeds, mustard seeds and garam masala powder (in this order). Fry 10 seconds, add to curry and stir. Serve.