In a casserole pan, brown the chicken pieces on all sides in 3 tbsp oil until golden - do this in batches. Remove and leave on one side, leaving the oil in the pan. Roughly chop the garlic, ginger, onions and chopped chillies together, then put into a processor with a dash of water and pulverize to a paste. Mix in the spices, with some salt and an extra good twist of pepper. Fry this paste in the casserole, stirring often so that it doesn’t catch, until it’s well softened and browned. Stir in the tomatoes and sugar, bring to a bubble, and simmer for about 20 minutes. Put the browned chicken and whole chillies into the pan with enough water so that the meat is almost covered. Cover the pan, then place in a 180°C/350‘F/Gas 4 oven and cook, stirring through once or twice, for about 40 minutes, until it is cooked through. It can now sit like this until you’re ready - just reheat it in the oven or on the hob. Eat with naan breads or rice, yoghurt and fresh coriander.