For the cream of Jerusalem artichoke soup, dice the cleaned mushrooms and sauté in butter for about 8 minutes. Boil the Jerusalem artichoke tubers until soft, peel and dice. Set aside.
Heat the chicken soup with the lemon juice and tarragon and simmer gently for 10 minutes. Remove the tarragon.
Puree the diced Jerusalem artichokes with a little chicken soup and add to the simmering chicken soup. Refine the soup with whipped cream and season to taste with salt and freshly ground pepper.
Serve the cream of Jerusalem artichoke soup in warmed soup plates. Garnish with the steamed mushrooms.