Bring 1 litre of water to the boil. Peel the onion and chop finely. Scrape the carrot and slice it. Mix the onion, carrot, thyme, cloves, peppercorns and bayleaf in the water. Add the meat as soon as the water boils. Turn down the heat and cook for about 45 minutes, till done. Skim the scum every now and then.
Remove the meat from the pan and sieve the stock. Dice the veal roast. Wipe the mushrooms clean and slice or halve them. Peel the shallots and divide them into four. Braise the mushrooms and shallots in 2 dl veal stock for 3-5 minutes. Then sieve and put the mixture to one side. Pre-heat the oven to 180ºC (356°F). Melt the butter and mix in the flour. Allow the roux to simmer for about half a minute. Add 2 dl. of the stock gradually, stirring well.
Put the vol-au-vent cases in the oven. Beat the egg yolk with the cream and wine. Pour some of the warm sauce into the cream mixture, then add this to the ragout. Stir the veal, mushrooms, shallots and parsley into the sauce. Add salt and pepper to taste. Heat thoroughly, without boiling. Dilute the sauce with stock if necessary.
Serve the veal ragout in the warm vol-au-vent cases and garnish with lemon segments.
* Replace the veal roast with veal breast but cook it for about 1½ hours.
* Use profiteroles instead of vol-au-vent cases.