Peel the celery, onions and apples and cut into small cubes. Melt the butter in the soup pot, sauté the celery, onions and apples in the pot. Deglaze with apple juice, fill up with vegetable stock, stir and bring to the boil. Reduce the heat and let everything simmer covered for about 30 minutes.
Peel the potatoes and slice them thinly. Heat 3 tablespoons of oil in a pan, add the potatoes and fry until golden brown, drain on paper towels.
Stir the mascarino until smooth and add to the warm soup. Mix with a whisk or blender. Season to taste with salt, ground white pepper and 1 pinch of nutmeg. Serve in soup plates and sprinkle with the potato chips.