Briefly roast the ingredients for the spice mix in a pan without fat over a low heat. Then grind in a mortar and pestle. Heat the oil in a large pan over a medium heat, fry the curry leaves for 2 minutes, add the onion and fry until golden brown. Blend the garlic and ginger into a paste and fry with the onions for 1 minute. Add the tomato purée and 100 ml water, stir in the spice mixture and bring to the boil. Stir in the chicken pieces, salt and a further 200 ml water. Cover and simmer for approx. 45 minutes. Infuse for 10 minutes before serving.