Fry half the onion in a little oil for a few minutes then add chicken – brown on all sides. Whizz the other half of the onion,1/4 cup water, the ginger and garlic to a fine paste and add this to the pan. Fry for a few minutes before adding the chillies, salt and pepper and stir well to mix.
Add the cayenne, vinegar, sugar and tomato. Stir and then add the yogurt and enough water to just cover. Add the curry leaves and simmer until chicken is cooked – time will vary depending on the cut of chicken you use, about 20 mins for breast and 35 for thigh fillets.