Leek and potato soup smells good, tastes good, and is simplicity itself to make. It is also versatile as a soup base; add water cress and you have a water-cress soup, or stir in cream and chill it for a vichyssoise. To change the formula a bit, add carrots, string beans, cauliflower, broccoli, or anything else you think would go with it, and vary the proportions as you wish.
Either simmer the vegetables, water, and salt together, partially covered, for 40 to 50 minutes until the vegetables are tender; or cook under 15 pounds pressure for 5 minutes, release pressure, and simmer uncovered for 15 minutes.
Mash the vegetables in the soup with a fork, or pass the soup through a food mill. Correct seasoning. (*) Set aside uncovered until just before serving, then reheat to the simmer.
Off heat and just before serving, stir in the cream or butter by spoonfuls. Pour into a tureen or soup cups and decorate with the herbs.