Possibly defrost the fish. ##Peel and wash potatoes## and cook in boiling salted water for about 20 minutes.
##Clean, wash and spin-dry the lamb's lettuce## ##peel and chop the onion## Mix apple juice, vinegar, salt and pepper. Mix half onion cubes and salad with marinade.
For the béchamel sauce melt butter. Dust with flour and sauté until light brown. Deglaze with milk and simmer for 5 minutes while stirring. Stir in sour cream. Season to taste with salt and pepper. Keep warm.
Rinse fish and pat dry. Season with salt and pepper. Heat 1 tsp. oil in a frying pan. Fry the fish for 3-4 minutes on each side.
Wash the dill and cut it finely. Drain the potatoes. Add dill to the sauce. Serve everything. Sprinkle with the rest of the onions. Add lemon.