Chargrill the skin of the eggplants by blackening them under a grill or on a gas hotplate. When thoroughly burnt, place in cold water to cool, then peel off the skin of the eggplants.
Cut up the eggplants and place into a large bowl. Mash well with a fork or potato masher. Stir in the yoghurt and onion. Season with cayenne pepper, salt and pepper to taste. Mix well and spoon into serving dish. Sprinkle with chilli and coriander before serving.