Cover the chicken with cold water and bring to the boil. Skim the foam from the surface. Add the vegetables and spices. Simmer over medium heat for 2 hours.
Remove the chicken from the stock and leave to cool. Debone the chicken and cut the meat into small cubes. Strain the stock through a fine sieve and remove the fat.
Prepare a roux with the butter and flour. Pour in about 1.5 l hot stock. Add the cream and lemon juice, then season to taste. Cook for 10 minutes, stirring constantly. Check the consistency of the sauce and thin it with a little water or stock if necessary.
Add the chicken and mushrooms, then bring to the boil.
Fill the warmed puff pastry shells with the mixture. Garnish with parsley or chives if desired.
Bouchée à la Reine has more flavour if canned mushrooms are used instead of fresh ones. Depending on taste, you can also add cooked veal or sweetbreads to the chicken mixture.