Peel and wash the potatoes and cut them lengthwise into halves or quarters. Heat the oil in a large coated pan. Cover the potatoes and fry them at medium heat for 12-15 minutes, season to taste
Clean, wash and cut the spring onions into rings. Fish wash, dab dry, cut into pieces. Sprinkle with lemon. Mix stock, yoghurt, starch and mustard, season
Add spring onions to the potatoes and fry for another 5 minutes. Stir in the yoghurt and mustard mixture and bring to the boil briefly. Season fish with salt and pepper. Place on the potatoes. Cover and let everything simmer at low heat for about 10 minutes. Arrange and possibly garnish