Wash the potatoes and cook in plenty of boiling water for about 20 minutes. Rinse under cold water, drain and peel
Clean and wash the pointed cabbage and cut it into thin strips from the stalk. Peel onion and cut into fine strips. Peel horseradish and grate finely. Heat butter in a large pan. Sauté the onion strips for about 4 minutes. Add cabbage and stock. Close the pan with a lid and let the cabbage collapse. Season with mustard and horseradish, except for something to sprinkle. Stew the cabbage covered for another 10 minutes. Season to taste with salt and pepper. Add potatoes
Arrange cabbage-potato pan and trout filets on plates. Sprinkle with remaining horseradish