Peel and wash all the vegetables (do not peel the courgette) and slice finely. Melt the butter in a saucepan and add the vegetables. Cook for 4-5 mins. On a low heat, stirring continuously. Add salt and pepper and pour in 1 litre of very hot water, bring to the boil and simmer for 25 mins. Chop the parsley and sprinkle over soup just before serving.