Set a large pot, about 25 centimetres (10 inches) in diameter, over a medium heat. Add the oil and, when it’s hot, tip in the onions and whole garlic cloves. Stir and fry for a few minutes, then cover. Cook for 15 minutes until brown, stirring occasionally and adding a splash of water, if necessary.

Increase the heat to high and add the plum tomatoes and a little of the juice from the can. Stir and mash for two to three minutes. Add the chilli powder, turmeric, ground coriander and cumin and the garam masala, mashing until you have a thick sauce. Mix in the salt and ginger.

Put in the chicken pieces and brown them on all sides for two to three minutes. Cover and cook over a low heat for 15 minutes, stirring occasionally. Increase the heat to high and add the spinach, milk and chillies. Mix well and cook over a medium heat for 15-20 minutes, stirring now and then and adding small amounts of water if the chicken seems to stick or brown too much. Serve.