Sweat the onion with the butter in a saucepan without colouring, until soft. Add the broad beans, together with the water and bring to the boil. Add whichever herb you have chosen, chopped fine (I recommend the use of savory), season with salt, sugar and pepper. When the beans are cooked, take out a tablespoonful or so, refresh on cold water, skin and reserve them. Puree the soup, either in a blender or through a sieve. Reheat to simmering point, stir in the cream, correct the seasoning and add the reserved beans. Serve hot with freshly cooked home made croutons.