Peel the celery root, onion, carrots and potatoes, finely chop. Cut the celery stalks into pieces.
Heat the oil in a saucepan, fry the celery stalks, 3 minutes. Add onions and carrots, cook 5 minutes. Add celery root and potatoes.
Pour in milk. Bring to a boil, reduce heat and simmer for 20 minutes. Pour the soup into a blender, puree. Return soup to saucepan, season with salt and pepper to taste. Bring to the desired temperature and serve. You can decorate with carrot chips.