Wash the chicken and pat dry. combine th eyogurt, tomatoes, cinnamon, cardamom, cloves, peppercorns, cumin, chilies, saffron, turmeric, cayenne, ginger, garlic and salt. Pour mixture over the chicken, turning the pieces until they are well coated. While they marinate, fry the onions gently in the butter and oil until light, golden brown. You may use either a large, heavy skillet or stew pot.
Remove the onioms. When they have cooled slightly, crush them with the back of a spoon. Return them to the pot or skillet, along with the entire contents of the marinating bowl. Simmer until chicken is tender, adding small amounts of water as necessary to keep contents from sticking. Garnish with fresh coriander and mint leaves, and serve with rice or indian bread.
Variation : In the last 10-15 minutes of cooking, toss in a handful of whole, pitted prunes and/or a dozen of wholes , pitted prunes and/or a dozen whole, peeled almonds. You may also add potatoes. If you do, chop them into pieces about 3 inches across, and boil them in water until soft but still firm.
Saute in oil to crisp the surfaces before adding them to curry in the last few minutes before serving.