This is more commonly known as Potage àla Reine. The name translates to "Queen's Soup".
- Mix the butter and flour and bring to the boil.
- Slowly add the warm stock and bring to the boil.
- Let the soup boil for another 10 minutes.
- Beat the egg with the cream or milk and slowly pour in some hot soup until the egg is thoroughly heated through.
- Then pour in the rest of the soup.