Wash and clean chicken pieces. Drain out water thoroughly.
In a bowl, marinate chicken pieces evenly with turmeric powder and salt. Cover and keep aside for half an hour.
Heat an iron kadai or a dry skillet on medium heat. Gently dry roast all the spice ingredients until fragrant and make a smooth paste in a small mixer bowl with 2 tbsp water. Keep aside.
In a wide bowl, take marinated chicken pieces with spice paste, shallots, garlic, ginger, vinegar, salt to taste (first add 3/4 tsp and check the taste) and water (up to the level of chicken pieces).
Cover with a lid and boil on medium to low heat for 15-20 minutes until the water (stock) has reduced to about 1.5 cups. Remove cooked chicken pieces from the pan and reserve the gravy (stock).
Heat oil in a wide pan. Add mustard seeds. When they crackle, add sliced onion and fry until it becomes golden in colour. Add curry leaves and fry again for 5 minutes on medium heat.
Now add chicken pieces without gravy and fry for 8 minutes until meat is lightly browned.
Add the reserved gravy, adjust salt to taste and cook again on low heat for another 10 minutes until the gravy becomes thick. Serve after half an hour so that all the flavours are absorbed. Serve with rice / pulao / chapati / appam / idiyappam / whole wheat bread.