Wash the fish fillets and dab them dry. Cut each fillet into three pieces, sprinkle with lemon juice and salt. Cover and put aside. Roughly dice the potatoes and cook in little boiling salted water for about 15 minutes. Cut Chinese cabbage into strips. Finely dice onion and cucumber.
Quarter apple, remove seeds and cut into thin slices. Heat 15 g fat in a frying pan and fry the drained fish fillets for about 4 minutes, turning them over until golden brown. Remove the fish from the pan. Lightly brown half the onion in the hot frying fat. Add apple, cucumber and capers. Deglaze with 150 ml stock and cream. Stir mustard and Biobin into the sauce, bring to the boil and simmer for about 2 minutes. Season sauce with salt, pepper and mustard. Place the fish fillets on the hot sauce and keep warm. Drain the potatoes, collecting approx. 50 ml of potato water and add it back to the potatoes. Warm the milk, add it to the potatoes as well and mash everything roughly.
Stir mustard and Biobin into the sauce, bring to the boil and simmer for about 2 minutes. Season sauce with salt, pepper and mustard. Place the fish fillets on the hot sauce and keep warm. Drain the potatoes, collecting approx. 50 ml of potato water and add it back to the potatoes. Warm the milk, add it to the potatoes as well and mash everything roughly. Season to taste with salt and nutmeg. Heat the rest of the fat in the pot and sauté the remaining onion in it, add the Chinese cabbage, braise well and deglaze with the remaining stock. Cover and simmer for about 3 minutes. Season vegetables with salt and pepper. Arrange fish with sauce, vegetables and mashed potatoes on two plates. Serve garnished with parsley
Season to taste with salt and nutmeg. Heat the rest of the fat in the pot and sauté the remaining onion in it, add the Chinese cabbage, braise well and deglaze with the remaining stock. Cover and simmer for about 3 minutes. Season vegetables with salt and pepper. Arrange fish with sauce, vegetables and mashed potatoes on two plates. Serve garnished with parsley