Potage Bonne Femme (Potato Leek Soup)

adapted from "From Julia Child's Kitchen"

Ingredients
3 tablespoons butter
3 cups of thinly sliced or minced leeks (white part only), or onion, or combinations of both if desired
3 tablespoons flour
2 quarts chicken stock
4 cups of diced peeled potatoes
1 teaspoon salt, white pepper to taste
1/3 to 1/2 milk, heavy cream or sour cream
3 tablespoons minced fresh chives or parsley

Directions
Melt butter over moderate heat, add leek & onion mixture, cooking slowly for 5 minutes. Do not brown. Blend in flour, again do not brown. Remove from heat, cool for a minute or two. Gradually beat in 1 cup of chicken stock (from the 2 quart total). Blend thoroughly with the flour and leek/onions. Add remaining chicken stock.

Add salt, pepper and potatoes. Bring to boil and simmer partially covered for 40-50 minutes until vegetables are tender. Remove from heat, prior to serving stir in cream by spoonful and top with chives or parsley.

Optional:
Mash the vegetables with a fork in the pan or potato masher. For a smoother texture put through medium blade of a food mill.

Note:
For ease you can place the leeks and onion mixture in food processor and pulse to about 3/8". Potatoes can be chopped in the food processor separately as well.
For a smooth texture upon the completion of cooking, I used an immersion blender.