Peel, wash and chop the potatoes. Wash, clean, quarter, seed and also finely dice the tomato. Peel and finely dice the onion. Wash the fish and dab dry. Sprinkle with lemon juice.
Mix flour and salt, turn the fish in it. Heat clarified butter in a frying pan, fry the plaice in it over medium heat for 3-4 minutes on each side. Meanwhile, heat oil in a small pan, fry onions and potatoes while turning, add tomatoes and deglaze with stock and wine.
Let simmer for about 6 minutes at low heat. Season to taste with salt and pepper. In the meantime wash parsley, dab dry and chop finely. Add parsley to the vegetables and mix in. Wash the cress and cut from the bed.
Pour the vegetables over the fish and sprinkle with cress. Serve garnished with chives and lemon wedges.