In a large pot, heat butter. Sauté leeks and celery for a few minutes. Add the apples and potatoes. Sauté for about 1 minute. Add broth and bring to a boil. Season to taste.
Simmer until vegetables are tender, about 30-40 minutes.
Puree and season to taste.
Garnish (not calculated in nutritional facts) : parsley and julienned apple