Preheat the oven to 200C/400F. Fry the onions in the oil in a flameproof casserole until translucent. Add all other ingredients except the meat, and half UK pint / 300ml water. Bring to a boil: add the meat. Put the casserole in the oven and braise the meat for 45 minutes, checking every 10 minutes to give it a stir and make sure there's enough water. When the meat is tender on the outside but still a little pink inside, take it out with a slotted spoon. Let the contents of the casserole cool a little. Then empty the contents into a blender or food processor and liquidize. This becomes your basic Balti sauce, and should be the consistency of thick soup. The meat is now ready for its final cooking in the balti.