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.

VARIATIONS:

Potate au Cresson (Water-cress Soup)

This simple version of water-cress soup is very good.

Serves 6 to 8 people

Ingredients are the same as for the leek and potato soup, omitting cream or butter enrichment until later and adding ¼ lb or about 1 packed cup of water-cress leaves and tender stems.

Follow the preceding master recipe, but before puréeing the soup, stir in the water cress and simmer for 5 minutes. Then purée in a food mill and correct seasoning. Off heat and just before serving, stir in 4 to 6 Tb cream or 2 to 3 Tb butter by spoonfuls. Decorate with the optional water-cress leaves.

Vichyssoise (Cold Leek and Potato Soup)

This is an American invention based on the leek and potato soup in the preceding master recipe.

Serves 6 to 8 people

Ingredients are the same as for the leek and potato soup with the addition of 3 cups peeled and sliced potatoes, 3 cups sliced white of leek, and 1½ quarts of white stock chicken stock, or canned chicken broth.

Simmer the vegetables in stock or broth instead of water as described in the master recipe. Purée the soup either in the electric blender, or through a food mill and then through a fine sieve. Stir in ½ to 1 cup cream. Season to taste, over salting very slightly as salt loses savor in a cold dish. Chill. Serve in chilled soup cups and decorate with minced chives.

Other Variations on Leek and Potato Soup:

Using the master recipe for leek and potato soup, a cup or two of one or a combination of the following vegetables may be added as indicated. Proportions are not important here, and you can use your imagination to the full. Many of the delicious soups you eat in French homes and little restaurants are made just this way, with a leek-and-potato base to which leftover vegetables or sauces and a few fresh items are added. You can also experiment on your own combinations for cold soups, by stirring a cup or more of heavy cream into the cooked soup, chilling it, then sprinkling on fresh herbs just before serving. You may find you have invented a marvelous concoction, which you can keep as a secret of the house.

To be simmered or cooked in the pressure cooker with the potatoes and leeks or onions at the start: Sliced or diced carrots or turnips; peeled, seeded, and chopped tomatoes, or strained canned tomatoes; half-cooked dried beans, peas, or lentils, including their cooking liquid.

To be simmered for 10 to 15 minutes with the soup after it has been puréed: Fresh or frozen diced cauliflower, cucumbers, broccoli, Lima beans, peas, string beans, okra, or zucchini; shredded lettuce, spinach, sorrel, or cabbage.

To be heated in the soup just before serving: Diced, cooked leftovers of any of the preceding vegetables; tomatoes, peeled, seeded, juiced, and diced.