Peel and rinse the potatoes and cut into very fine grates with a fine grater. Stir in sour cream or possibly natural yogurt on the spot so that the potato rasps do not discolor. Put the potatoes into a sieve and drain the potato juice.
Season potato mixture with salt, perhaps add 1 pinch of nutmeg and fold in an egg. Heat some olive oil in a frying pan, then add the butter. Using 1 tbsp potato mixture, make flat patties in 2 frying pans, dividing evenly, and fry on both sides for 10 minutes until golden.
Parsley root and parsnips can be prepared according to the same recipe.