Clean, peel, wash and cut the celeriac into pieces. Clean and wash the celery. About 3/4 in pieces, cut the rest into thin slices. Put celery slices and celery leaves aside for garnishing.
Peel and chop the onion. Peel, wash and chop the potatoes.
Heat 2 tablespoons of butter in a wide saucepan. Add onion, celery pieces and potatoes and stir-fry for about 4 minutes at low heat until colourless. Pour in broth. Season with salt, pepper and nutmeg.
Simmer at medium heat for about 20 minutes.
Meanwhile chestnuts roughly chop. Melt 1 tsp. butter with sugar in a pan. Caramelise the chestnuts for about 2 minutes while turning. Pour onto a flat plate. Pour the cream into the soup, puree the soup finely.
Add the celery slices and leave to stand for about 5 minutes. Season to taste with salt, pepper and nutmeg.
Wash the chives, shake dry and cut into fine rolls, except for a few stalks for garnishing. Serve the soup with chestnuts. Sprinkle with chive rolls and garnish with chive stalks and celery leaves.