Peel and chop the onion. Clean the celeriac, set aside 1 medium stalk of celery green. Peel, wash and chop the celery and half the potatoes. Heat 1 tablespoon of oil in a large pot. Sauté the onion until transparent. Fry potato cubes and celery briefly. Season with salt, pepper and 1 pinch of sugar. Deglaze with 800 ml water and bring to the boil. Stir in stock. Simmer covered for 15-20 minutes.
In the meantime, peel the rest of the potatoes, wash them and cut them into cubes of just under 1 cm. Heat 1 tablespoon of oil in a large frying pan. Fry the diced potatoes for 10-15 minutes over medium heat until golden brown. Season with salt and nutmeg. Wash the celery green, shake dry and cut finely.
Slide potatoes to the edge of the pan and heat 1 tbsp. oil in the pan. Fry the ground pork in it until crumbly. Pour cream into the soup, bring to the boil again briefly and puree finely with a hand blender. Season soup again and serve. Sprinkle with potato croutons, minced meat flakes and celery green.