Remove fat from the chicken and then salt and pepper it. Sprinkle with chili powder. Add yogurt and mix well until the chicken is covered liberally with yogurt. Use your hands. Set aside for 1 hour before cooking. If kept in the refrigerator, set aside for at least 4 hours. Heat oil in a large heavy pan. When oil is hot, add mustard seeds, if you are using them. Add cloves, cardamom, and coriander seeds and fry for 30 seconds. Add the onion and fry for two minutes until the onion beings to turn brown. Lower heat to medium. Add the ginger and garlic paste and fry for 4-6 minutes. Add mustard powder, if using it, add Garam Masala, and add cumin powder. Brush excess yogurt off the chicken and put it in a large pot. Add ingredients from the frying pan. Cook uncovered over high heat for 4 minutes. Reduce heat to low and cover. Cook for 25 minutes or until the chicken is tender, stirring every 5 minutes. note: When chicken is cooked with a cover on the pot, it releases water that becomes a part of the sauce. If after 10 minutes, there isn't enough sauce in the pot, add 1/4 cup water. Conversely, if there is too much liquid in the pot, cook uncovered until the liquid evaporates. Note: There are several variations to the above recipe: Leave out the yogurt. Add 1/4 cup of water just before turning the heat to low and covering the pot. Boil two potatoes for 10 minutes before slicing them thinly. Add sliced potatoes to the pot when you start cooking the chicken. This variation is usually called "Malai Chicken" or literally "creamy" chicken. Leave out the yogurt. When the chicken is 3/4 done, add one small can of tomato paste. Just before removing add a small carton of whipping cream, and cook for a few minutes.