Prep:

Cup of Yum
1. Preheat the oven to 425F (220C).

Make the filling:

1. Heat a large pan over medium-high heat. Once hot, add the oil and spread it around the pan. Add the onions and celery, and cook them while stirring frequently for 3 to 5 minutes until the onions have softened and are translucent. Season it with the garlic powder, paprika, and poultry seasoning, and stir.
2. To the pan, add the mixed vegetables and cooked chicken pieces. Stir to combine. Pour the chicken stock into the pan and stir to cook and heat everything through for about 5 minutes. Add the milk, stir, and reduce the heat to medium-low, letting it cook while it comes up to a simmer.
3. Make a slurry by mixing the cornstarch and water in a small dish. Add it to the simmering filling in the pan and combine. Cover the pan with a lid and continue simmering the mixture for 3 minutes and turn off the heat.

Assemble:

1. Place one pie crust in a 9-inch pie plate.
2. Use a ladle to transfer the filling from the pot into the prepared pie dish. Cover the pie plate with the second pie crust, sealing the edges with your fingertips. With a sharp knife, make a cross-shaped opening at the top of the pie to let the steam vent out. Lightly brush some milk over the top of the pie to make it shiny.
3. Fold some foil into a 3-inch wide strip and wrap the pie's edges to prevent them from browning too quickly. They can be removed in the last 5 minutes of baking.

Bake:

1. Bake in the preheated oven for 25 to 30 minutes, until the top of the pie crust is golden brown.
2. Remove the baking sheet from the oven and allow the pie to rest for 10 minutes before serving.