Peel and slice up the vegetables and sprinkle them with the sugar and salt, and put them into a saucepan with the butter, and sweat for five minutes. Pour over the boiling stock and stir until it boils; boil slowly for an hour, then rub through a sieve. If it is too thick, reduce it with a little more stock or milk, return to a saucepan, and bring to the boil. When tomatoes are in season slice up two with the other vegetables; these will make the soup a good colour and improve the flavour.
Time: 1 hour.