Heat the oil in a pan and sauté the onions and celery root for about 30 minutes, until softened. Stir constantly to avoid burning. Add mushrooms, potato, and celery. Sauté for another 10–15 minutes.

Cover the vegetables with chicken or vegetable broth and allow to simmer until all vegetables have softened. Add salt and pepper. If too thick, add water.

If desired, add some white wine into the soup before serving for a gourmet effect. Top with toasted walnut pieces and fresh parsley.