Peel, wash and halve the potatoes and cook in boiling salted water for about 20 minutes. Clean broccoli and cauliflower, cut into florets from the stalk and wash. Peel, wash and slice carrots. Bring 1 litre of salted water to the boil, add vegetables, bring to the boil and simmer for about 5 minutes
Meanwhile, boil eggs in boiling water for 8-10 minutes. Pour vegetables into a sieve, collect the stock. Melt the fat in a pot. Stir in flour and sweat briefly. Add 350 ml vegetable stock and milk while stirring. Bring to the boil, boil for 1-2 minutes and season with salt and pepper.
Stir in mustard. Add vegetables to the sauce. Wash the chervil, shake dry and chop, except for something to garnish. Drain eggs, quench and peel. Arrange vegetables, eggs and potatoes on plates. Sprinkle with chervil and garnish