Remove the skin from the (cooked) chicken, and remove the meat from the bones.
Cut the chicken into bite sized pieces, and set aside.
Preparing the base
Add the gelatin to the stock and set aside.
Peel the carrots, and chop the celery and carrots into bite sized pieces roughly the same size.
Peel, and finely dice the onions.
Heat a pan over low heat. Once heated, add the oil.
Add the celery, onions, and carrots, and stir frequently until they begin to soften. Ten to fifteen minutes.
Once softened, add the flour, and continue to cook for a couple of minutes until the flour begins to brown.
Add the gelatin and stock, and stir to combine. Add the milk, and bring the to a light boil.
Once it begins to boil, add the frozen peas, and bring back to a boil.
Once it comes to a boil, add the chicken. Stir to mix thoroughly,
Add the salt and pepper (to taste).
Pour the contents into a large casserole dish, and place it in the fridge to cool.
Building the pot pie
Lay the thawed puff pastry in the pot pie pan, making sure to fill the pan. Make sure not to punch the puff pasty.
Fill the pastry with the cooled chicken mixture.
Fold the pastry corners towards the centre creating a square of pastry.
Fold the corners again towards the centre.
Place the formed pot pie in the fridge until ready to cook. Or, you can freeze it at this point.
Cooking the pot pie
Pre-heat oven to 375°F
Place the pot pies in the oven on a cookie sheet and cook for 30 to 45 minutes, or until the pastry begins to brown. Depending on how many you are cooking, the size of the pot pies you are making, and your oven, the time will vary.
Once the pot pies have browned, remove from the oven and allow to cool for a few minutes, and serve.