Peel, wash and dice the celery and parsley root, except for some celery for garnishing. Peel and finely dice the onion. Heat fat in a pot and sauté prepared vegetable cubes for about 5 minutes while stirring. Add stock, bring to the boil and simmer for about 15 minutes
Finely dice the bacon and fry it in a pan without fat for approx. 5 minutes until crispy. Chop the chestnuts and roast them in the bacon fat for approx. 5 minutes while turning
Add the milk and cheese to the soup, bring to the boil and finely puree the soup with a hand blender. Season to taste with salt and pepper
Cut the remaining celery into wafer-thin slices. Heat oil and fry celery slices for about 3 minutes until crispy. Arrange soup, chestnut and bacon cubes in plates. Garnish with celery slices and parsley