1 1/2 c. white part of leeks
1/2 c. onion
1 tbsp. butter
3 c. peeled potatoes
3 c. hot water
3 c. hot milk
1 tbsp. butter
2 egg yolks (opt.)
1/2 c. cream (opt.)

Discard green tops and roots from about 4 leeks; clean white part well, cut them into 1/3" dice. There should be about 1 1/2 cups. Peel and dice 1 medium onion, about 1/2 cup. Melt 1 tablespoon butter in 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" dice, about 3 cups. Add the potatoes, 3 cups hot water and simmer the soup, covered, for 30 to 40 minutes, or until the potatoes are very soft.

Force the mixture through a sieve or food mill. Bring the soup back to a boil, stirring constantly to prevent it from scorching, and add 3 cups hot milk and 1 tablespoon butter. For a richer soup, beat 2 egg yolks lightly with 1/2 cup cream, gradually stir in 1 cup of the hot soup into them and return the mixture to the kettle, stirring briskly. Bring the soup just to the boiling point, stirring constantly, but do not allow it to boil. (NOTE: Soup can be frozen in cartons, but eliminate the milk or cream as it does not thaw smoothly. When thawing, add milk and cream to the consistency desired.)