Peel and wash the celery and potatoes and cut them into small cubes. Peel and finely dice the onion. Heat the fat in a pot. Sauté the onion for about 4 minutes while turning. Add celery and potato to the onion cubes. Steam in a closed pot for about 5 minutes. Stir in between
Peel and quarter the apple, remove the core and dice the flesh. Add stock and apple to the pot, bring to the boil and simmer for about 20 minutes. Season to taste with salt and pepper
Cut the cheese into pieces and put them into the pot, except for something to sprinkle on top. Wash parsley, shake dry, pluck leaves from the stalks and chop. Arrange the soup and sprinkle with the remaining cheese and parsley