Wash the fish, pat dry and cut into 4 pieces. Sprinkle with lemon juice and let it stand for a short time. Peel, wash and roughly grate the potatoes. Mix with egg and season. Salt the fish. Spread the grated potatoes as a cap and press well
Heat the oil in a coated pan. First fry the fish on the potato side for about 10 minutes. Turn carefully and continue frying for 2-4 minutes
In the meantime clean, wash and cut the leek into pieces. Bring approx. 600 ml water and broth to the boil. Cover the leeks and stew them for 10-12 minutes. Then drain, catch the vegetable water
Heat the fat in a pot. Sweat flour in it. Stir in vegetable water and cream. Bring to the boil and simmer for about 5 minutes. Wash the herbs and pluck or roughly chop them, except for a little bit for garnishing. Stir mustard into the sauce and season to taste. Heat the leek in the sauce. Arrange everything, garnish with the rest of the herbs and lemon. Goes well with bread