Finely puree the cooked spinach, using a food processor or electric blender, or mince it with a knife on a chopping board. Set aside.
Preheat the oven to 325 degrees Fahrenheit.
Heat 2 tablespoons of oil in a large frying pan over high heat until very hot. Pat the meat dry on paper towels (or it will not brown) and add to the pan. Brown the meat, turning and tossing the pieces, until nicely seared on all sides. This is best done in batches so that the frying pan is not overcrowded. As each batch is browned, transfer to a heavy-bottomed casserole.
Add the remaining 4 tablespoons oil to the frying pan and add chopped onions. Reduce heat to medium-high, and fry them until they turn light caramel brown (about 25 minutes). (Do this carefully and patiently to avoid burning any of the onions. If in doubt, reduce the heat and take longer.) Add garlic and ginger and fry for an additional 2 minutes. Add cumin, coriander, and tumeric, and stir rapidly for 15 seconds. Add tomatoes and chiles, and continue frying until the tomato is cooked and the entire mixture is turned into a thick, pulpy paste (about 3 minutes). Add yogurt or sour cream, and immediately turn off the heat. When slightly cool, puree in an electric blender or food processor, and add to the meat in the casserole.
Place a double layer of cheesecloth, about 6 inches square, on the work surface. Put cinnamon, cardamom, cloves, and bay leaves in the center, bring up the four corners of the cheesecloth to wrap the spices, and tie them to form a bag. Crush the bag slightly with a wooden mallet or any heavy tool to break up the spices. Add the spice bag to the casserole.
Add 4 cups of boiling water along with the salt, and stir to distribute the meat into the sauce. Place a piece of aluminum foil on top of the casserole, and cover tightly with the lid. Bring the contents to a boil on top of the stove.
Place the casserole in the middle level of the oven for 2 1/2 hours. Alternatively, it may be cooked on top of the stove over low heat for 2 to 2 1/2 hours or until the meat is fork tender.
Remove the casserole from the oven (or turn off the stove) and take off the lid. Remove the spice bag, squeeze hard to extract as much juice as possible, and discard the bag. Add the cooked spinach and garam masala and blend well, being careful not to break the fragile meat pieces. Cover the pot, return it to the oven or stove, and cook for 5 minutes more. Turn off the oven, and let the pot remain undisturbed for an additional 10 minutes. Check for salt, and if the sauce lacks adequare glaze, stir in a few tablespoons of oil.
This dish, just like any other braised dish, tastes better with keeping. It is particularly good if made a few hours in advance, and allowed to rest at room temperature before being reheated and served. This dish keeps well in the refrigerator for up to 2 days and also freezes well. Defrost throughly before reheating. To reheat, gently simmer over low heat until warmed through. Before serving, taste for salt, and if necessary, fold in a little garam masala.
continued in part 2