Jerusalem artichoke soup

Jerusalem artichoke, also known in English as "sunchoke" [jordärtskocka in Swedish and topinambour in French] and celeriac, also known as celery root, give a distinctive taste to this soup. Next time though, I'll add more stock and less cream than in the recipe below.
For 4-6 people: 500 gr (~ 1lb) Jerusalem artichokes, 2 large baking potatoes, 150 gr (~0.3 lbs, or about half a celeriac) celeriac, 2 shallots, 1 liter (~4 cups) chicken stock and 4 dl (~1.5 cup) heavy cream. Peel and chop all the roots, saute them for 5 minutes, then add the chicken stock and simmer, covered, for about 30 minutes. Then add cream and simmer an additional 15 minutes before mixing the soup to smooth consistency. Garnish with crumbled bacon that has baked in the oven 10 minutes at 200 C/ 400 F.