This has become a traditional French soup, generally served cold but it's just as delicious served hot. It was developed and named by a French Chef working at the Ritz in New York city in 1917 who developed his own mothers leak and potato recipe into a rich and delicious cold soup. It was named after the town of Vichy which was the closest one to where he came from. It's basically a leek and potato soup which is cooled down and then cream is added. I only found out recently that it's often served with a hard boiled egg in the middle. Sounded a little strange but when I tried it, it really was delicious. Here's a recipe I found in a book of my grandmothers. You can choose to serve it hot or cold. (serves 4)

1 medium red onion finely sliced
2 medium leeks finely sliced
40g Butter
150g Potatoes peeled and cut into small chunks
800 ml hot chicken stock
120ml double cream
2 hard boiled eggs
croutons and olive oil to serve

1. Melt the butter in a large saucepan and add the onion. Fry until the onion is soft but not brown. 
2. Add the leeks and leave to soften for 10 minutes over a low heat. Stir regularly.
3. Add the potato then the hot chicken stock. Bring to the boil then simmer for 30 minutes, or until the potato is soft. 
4. Process until smooth preferably with a hand blender stick. Then pass the soup through a sieve to smooth out any remaining lumps.
5. Place in the fridge for at least an hour, or until ready to use.
6. When serving, whisk in the double cream, place half an egg face down in the middle of each of the soup bowls,  and then pour the soup around the egg. Garnish with croutons and a drizzle of extra virgin olive oil, plus a little ground pepper.