Melt butter in a large, heavy bottomed saucepan over medium heat. Add the leek, celery and fennel; cook, stirring, until soft but not browned.
Add Jerusalem artichokes, Bouquet Garni, and chicken stock. Cover and bring to a boil; reduce heat and simmer until artichokes are tender. Let cool for 10 minutes.
Remove Bouquet Garni. Add cream, purée in samll batches until smooth. Return soup to the pot; reheat gently. Season to taste with salt and pepper. Serve in warmed soup bowls, garnished with deep fried parsnip chips. Prepare them as for potato chips.Servings: 4