I usually make this soup with two leeks, and three Yukon gold potatoes sautéed in olive oil, and then adding chicken stock and water to cover (and seasoned to taste with salt and pepper). However, to be fair to you, I am enclosing Alice Waters recipe (with her precise measurements) and include my comments.

Ingredients:

2 pounds of leeks

3 Tablespoons butter or olive oil

1 pound of Yukon Gold potatoes, peeled, halved or quartered, and sliced

*6 cups chicken stock (I use half stock, half water.)

*2 thyme sprigs (or a teaspoon of dried thyme)

*1 bay leaf

*2 Tablespoons chopped Italian parsley

salt, pepper to taste

lemon slices (optional) or champagne or white wine vinegar (optional)

Preparation:

1. Trim off the root end and the tough upper greens from leeks. Cut the trimmed leeks in half lengthwise and slice thin. Rinse in a bowl of cold water. Lift the leeks out of the water to drain. Continue rinsing until no dirt remains.
2. Melt butter (or oil) over medium heat in a heavy-bottomed pot.
3. Add the leeks along with thyme, bay leaf and salt. Cook until soft, about 10 minutes.
4. Add sliced potatoes and cook for 4 minutes.
5. Add chicken broth and water. Bring to a boil and turn down to a simmer. Cook until vegetables are tender, but not falling apart, about 30 minutes.
6. Check seasonings and adjust to taste. Remove bay leaf and thyme before serving. (If you used dried thyme, you won’t need to remove it.)
7. If you plan to purée the soup, do so now. Garnish with parsley and freshly ground black pepper and serve.

Note: Definitely purée the soup. A splash of vinegar can be added before serving, or garnish with a fresh lemon slice.

*The bay leaf, thyme, and parsley are optional.

Alice Waters suggests to stir in 1/3 cup heavy cream before serving. I have never found this necessary.