Put the meat in a pan with just enough water to cover. Bring to the boil and remove the scum. Add the onions, cinnamon stick and salt and pepper, and simmer for about 45 minutes until the meat is tender, adding more water if necessary.
Heat the yogurt in another pan. Before it gets too hot, mix the cornflour with a few tablespoons of water in a cup and stir it into the yogurt to stabili