- Chop the celery stocks and garlic; cut Jerusalem artichokes into chunks.
- Heat the butter in a soup pot over medium-high heat and cook the onions and celery until soft, about 5 minutes. Do not brown them. Add the garlic and sauté for 1 minute. Sprinkle with salt.
- Add the Jerusalem artichokes and the chicken stock to the pot and bring to a simmer. Reduce the heat to low, and simmer, covered, until the Jerusalem artichokes begin to break down, 45 minutes to an hour.
- With the help of immersion blender or upright blender; puree the soup. If using an upright blender, fill the blender bowl up only to a third of capacity at a time, if the soup is hot, and hold down the lid while blending. Alternately, you can push the soup through the finest grate on a food mill, or push it through a sturdy sieve. Add salt to taste.
- Sprinkle with freshly grated black pepper to serve.