1Heat 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.
3Add the artichokes and the vegetable 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.
5Using blender or upright blender, purée 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.
7Alternately, you can push the soup through the finest grate on a food mill, or push it through a sturdy sieve. Add salt to taste.