Clean and wash spring onions and cut into fine rings. Mushroom risotto, eggs and spring onions, up to 1 tbsp. to sprinkle, mix well.
Heat the oil in portions in a large frying pan. Add 3-4 patties of the risotto mixture with a tablespoon, flatten it a little bit and bake it on each side for about 2 minutes until golden brown. Remove and keep warm.
Bake about 10 Rösti from the remaining mass in the remaining oil.
In the meantime, mix sour cream, horseradish, lemon peel and lemon juice. Season with salt, pepper and 1 pinch of sugar. Serve the Rösti with salmon and sour cream. Serve sprinkled with the remaining spring onions.