Dice the celery, one of the onions, 2 cloves of garlic, and the thyme.
Boil these, with the young hen, in water to cover, until the hen is tender.
Boil the chicken slowly; quick boiling will toughen the meat, but slow boiling tenderizes it.
It should take from 3 to 4 hours to get the chicken properly tender.
Let the chicken stock cool.
Remove the chicken from the pot, take the meat from the bones, and cut it into small pieces as for Chicken a la King.
Set aside.
Chop fine 1/2 large onion or 1 medium sized one (the juicy yellow kind is best) and brown it in the butter, ever so slowly, so that it stays soft when it turns golden brown.
Add 1 large garlic clove (or 2 small ones), also chopped very fine or put through a garlic press.
Brown slightly.
Add the flour and brown a bit more.
Then add 3 cups of wanned chicken stock, the chopped parsley, and Kitchen Bouquet.
Add the cut up chicken and let simmer until the gravy is thickened.
Add the wine and mushrooms.
Salt and pepper to taste about 1/2 teaspoon salt and 1/8 teaspoon pepper will be a good starter.
Just before serving, heat the patty shell thoroughly in the oven and then pour the hot chicken filling into the shell, and cover with the top crust of the patty.