Soupe Bonne Femme

Remove the green tops and roots from 4 leeks, clean them well, and cut them into 1/3-inch dice. There should be about 1 1/2 cups. (If there are no leeks available, use 2 onions). Peel and dice 1 medium onion. There should be 1/2 cup. Melt 1 tablespoon butter in a large soup kettle, add the leeks and onion, and cook them slowly, covered, for a few minutes, or until they are soft but not brown, stirring occasionally with a wooden spoon. Cut 4 or 5 peeled potatoes into 1/2-inch dice. There should be about 3 cups. Add the potatoes, 4 cups hot water, and 2 teaspoons salt to the kettle, and simmer the soup, covered, for 30 or 40 minutes, or until the potatoes are soft. Add 2 cups hot milk and 1 tablespoon butter. Taste the soup and correct the seasoning with salt.

Source: Gourmet's Basic French Cookbook: Techniques of French Cuisine