Char the skin of the aubergines over the flame of a gas hob, under the grill or on a barbecue, using flameproof tongs. Put them in a bowl of cold water for 2 mins, then peel off the skin. Cut off the aubergine stems and slice into small pieces. Set aside.

Heat the oil in a medium saucepan over a medium-low heat, then add the onions. Cook until soft and golden brown, about 10 mins. Stir in the garlic and cook for a few seconds. Blitz the tomatoes to a smooth sauce in a food processor, then tip into the pan. Cook for 2 mins, then add 1 tsp salt, the chillies and garam masala. Cook for 2 mins more.

Add the aubergines to the sauce and cook over a low heat for 15 mins, then use a spoon to crush the aubergine to a pulp. Cook for a further 15 mins, adding a little water if it becomes too dry. Serve with roti (see recipe, below).