For the Jerusalem artichoke foam soup, first boil the Jerusalem artichoke tubers with the skin. Peel the tubers, set aside two nice pieces for the chowder and cut into rough cubes.
Peel and chop the onion and sauté in oil with the Jerusalem artichoke pieces. Deglaze with vinegar, clear soup and whipping cream. Stir the soup well and pass through a sieve. Blend with remaining whipped cream.
Sauté the remaining Jerusalem artichoke pieces in a frying pan with a little oil, season with salt and pepper, sprinkle with parsley and pour into the soup plates.
Arrange the Jerusalem artichoke soup in the prepared soup plates and serve.