Heat the coconut milk in a saucepan with the curry paste, stirring to mix well. Add the stock and then the aubergines, sugar, salt, fish sauce, galangal or ginger and mushrooms.
Bring to the boil and cook, stirring, for 2 minutes. Add the green pepper, lower the heat and cook for 1 minute. Serve in a bowl, garnished with the basil leaves and drizzled with coconut milk. Discard the piece of galangal or root ginger before serving.