Clean and wash spring onions and cut into fine rings. Radishes clean, wash and cut into cubes. Put 1-2 tbsp. spring onions and radishes aside for garnishing. Mix quark, milk, remaining radishes and spring onions, season with salt, pepper and sugar.
Clean, wash and drain the spinach and put it in a bowl. Pour boiling water over it, let it stand for about 1 minute. Remove, rinse in cold water and drain. Squeeze out the spinach and chop coarsely.
Peel, wash and coarsely grate the potatoes. Add egg, flour and spinach and mix. Heat oil in portions in a pan. Fry about 20 small Rösti out of the potato mixture in portions until golden brown.
Remove the finished Rösti and keep warm. Arrange the Rösti and quark on plates. Sprinkle with sprouts, spring onions and radishes.