Yield: 2 quarts


  • 2 Tablespoons butter
  • 3 cups sliced leeks, white and palest green, trimmed and rinsed (from 12 ounces untrimmed leeks)
  • 1 ½ cups sliced onions (about 6 ounces, or 2 medium onions)
  • 2 Tablespoons flour
  • 6 cups water
  • 4 cups peeled, diced potatoes, preferably russets, cut into 2-inch chunks (about 1 ½ pounds)
  • 1 ½ Tablespoons salt, or to taste
  • ½ Tablespoons freshly ground white pepper, or to taste

For serving:

Any of these enrichments and garnishes: For a rich finish, stir any of the following into mashed or pureed soup base: 2 or more tablespoons of unsalted butter; ½ cup or more heavy cream or sour cream.

To garnish, scatter any of the following over each serving: buttered croutons; fronds of fresh chervil; chopped fresh chives; chopped fresh parsley. Or add a spoonful of sour cream or crème fraîche, in a swirl or a mound.

Special equipment:

A large, heavy-bottomed 3- or 4-quart saucepan with cover

Melt the butter in the saucepan over moderate heat. Stir in the leek and onion pieces to coat with butter, cover the pan, and reduce the heat. Cook slowly, stirring occasionally, for 10 to 15 minutes, until the vegetables are very soft but not colored. Uncover, sprinkle on the flour, stir to distribute it well, and cook for 2 minutes over moderate heat. Remove from heat and let cool for a moment.

Then, stirring continually, gradually pour in 1 ½ cups of the water and bring to the simmer. When the liquid is smooth and starts to thicken, stir in the rest of the water, then add the potatoes and season with salt and pepper. Quickly heat the soup to a gentle boil, cover the pan, and lower the heat. Simmer for about 20 minutes, until the potatoes are tender. Correct seasonings.

To serve, mash, blend, or purée the soup to the desired consistency and adjust the seasonings. Garnish or vary the soup with additional ingredients as suggested above.

To store the soup, let cool uncovered, then refrigerate or freeze.