Put the ginger, garlic and chillies in a blender along with 4 tablespoons water and blend until smooth. Slice the onions into very fine half-rings. Grind the coriander seeds to a coarse powder. Finely grate the tomatoes.

Put the oil and butter in a large, wide, heavy-lidded pan and set over a medium–high heat. When hot, add the onions. Stir and fry, turning the heat down to medium as needed, until the onions are a medium brown. Add the ginger–garlic mixture. Stir and fry on a medium heat for 3–4 minutes. Add 250ml (8fl oz) water, as well as the cayenne pepper, coriander, salt, turmeric, tomatoes and natural yoghurt. Bring to the boil on a medium–high heat. Cook, stirring frequently, until the sauce is thick and the oil separates from it. Add the quail. Stir and fry for 3–4 minutes. Cover tightly, reduce the heat to low, and braise gently for 1 hour and 15 minutes or until the quail are tender. They should cook in their own juices. If they dry out, add a few tablespoons of water. Turn the birds around and stir gently every 6–7 minutes. Sprinkle over the garam masala 5 minutes before the cooking ends and stir it in.