Peel and dice the celery, potatoes, carrots and onions.
Sweat briefly in a saucepan with a little oil. Add the stock and simmer covered for about 15 minutes until everything is done.
In the meantime, if you want, you can still dice bread, or even bread that has already hardened, and fry it in the pan. Add the croutons to the soup before serving. That spices up the whole thing a bit.
When the vegetables are soft, puree everything, bring to the boil again and add the cream or milk. Puree again until the soup becomes a little frothy. Season to taste with salt, pepper and nutmeg.