Peel, wash and slice the potatoes. Heat 2 tablespoons of oil in a frying pan. Cover the potatoes and fry them for about 10 minutes. Clean, wash and slice the onions. Whisk egg and 1 tbsp. cold water and season with salt and pepper.
Wash the fish, dab dry and cut into cubes. First turn in 3 tablespoons of flour, then in the egg. Fry fish in 2 tablespoons of hot oil for about 5 minutes. Take out. Fry bacon in hot frying fat until crispy. Add spring onions and fry briefly.
Sprinkle with 1 tbsp. flour and sauté briefly. Deglaze with stock and cream. Bring to the boil and simmer for about 5 minutes. Fry potatoes open for another 10 minutes until crispy. Season with salt and pepper. Stir mustard into the sauce.
Season to taste with salt and pepper. Heat the fish in the sauce, fold in the fried potatoes and serve. Garnish with parsley.