Peel and halve the onion. Peel 2 carrots and cut into large pieces. Wash the meat and put it in a pot. Add prepared ingredients and peppercorns. Bring to the boil covered with water.
Salt and cover and cook over medium heat for about 1 1/4 hours. In the meantime peel, wash and halve the potatoes. Cook in boiling salted water for about 15 minutes. Peel, wash and cut the rest of the carrots into pieces.
Clean the cauliflower, wash it and cut it into florets. Clean and wash the mangetouts. Boil 1/2 litre of salted water. Cook mangetouts for about 3 minutes, carrots and cauliflower one after the other for about 7 minutes.
Store vegetable water. Melt the fat. Sweat flour in it. Deglaze with 200 ml vegetable water, 200 ml meat stock and cream. Boil up while stirring constantly. Season to taste with salt, pepper, horseradish and lemon juice.
Warm up prepared vegetables in it. Cut the meat into slices and arrange with the vegetables. Pluck the chervil and sprinkle over it.