Place the chicken in a saucepan with 2 cups water. Bring to a boil and then simmer till cooked through (about 20 minutes).
When cool, remove the chicken pieces, RESERVING the cooking water, and mix the milk and the stock (water chicken was cooked in) together and make up to 2 cups adding more water if required.
Heat the ghee in a heavy based pan on medium heat and add the cumin seeds, poppy seeds and peppercorns, taking care not to burn. When they splutter, add the ginger and garlic, and sauté till a little darker in color.
Add the salt and ground cashew paste and stir well to mix. Add to this the chicken, the stock and milk mixture and bring to a boil.
Add the cornflour mixture, bring to a boil again, then simmer for 2 minutes.
Add the vinegar, sugar and half the coriander leaves, mix and serve hot garnished with the rest of the coriander leaves. Serve with basmati rice.