Food of the World - Leek and Potato Soup

Apparently, it can be served hot or cold. Hot version is traditional French, and cold version is called Vichyssoise, as it is believed that it has been served for the first time in Ritz-Carlton Hotel in New York by a French chef from Vichy.

50 g butter
1 chopped onion
3 leeks, white part only, sliced
1 celery stalk, finely chopped
1 garlic clove, chopped
200 g potatoes
750 ml chicken stock
220ml single cream

Melt the butter in a large saucepan and add the onion, leek, celery and garlic. Cover the pan and cook over low heat for 15 minutes, stirring. Add chopped potatoes, stock and bring to boil. Reduce the heat and leave to simmer for about 20 minutes (covered). Allow to cool a little before puréeing in a blender.
Return to clean saucepan, bring the soup gently to boil and stir in the cream. Season with salt and white pepper and reheat without boiling.
Few tips: you can also make it without celery and / or without cream (a healthier option?)