Preparation / Directions:
Heat butter in kettle or large saucepan. Shred leeks and add to pan. Cook until leeks are slightly browned. Add potatoes, water, and salt. Bring to boil.
Cover and simmer for 30 minutes, or until potatoes are tender. Strain. Mash vegetables. Stir cooking liquid into mashed vegetables and return to pan. Bring to boil.
Stir in milk and yolk. Bring back to boiling point but do not allow to boil.
Serve hot with fried French bread, or chilled without bread.
Recipe Source: THE ART OF FRENCH COOKING by Fernande Garvin