Roll out one pie crust in a large circle so that it will fill the bottom and sides of a 9 inch pie plate. Be sure that the circle is large enough so that you have about 1/4 inch extra around the edges.
In a large bowl combine all of the ingredients and mix well. Be sure that all of the cornstarch is mixed in well. Pour chicken and vegetable mixture into pie crust.
Roll out remaining pie crust. This will become the top of your potpie. Be sure that your top crust is large enough to completely cover the contents of the potpie and go over the edge of the pie plate about 1/4 inch all around.
If you have excess pie dough on any side use scissors to trim. Pinch and crimp your top and bottom pie crust together creating a seal around your potpie. Use a knife and cut 4-6 slits into your top pie crust.
If you are going to freeze your pot pie for later use, wrap your potpie in parchment paper. Using a marker or pen write the date that you prepared your potpie on the top of the parchment paper. Next, completely cover your parchment paper wrapped pot pie with plastic wrap. Place in the freezer. Potpie can be kept in the freezer for up to 4-6 months.
Pre-heat oven to 400°. Place baking sheet in oven while it is pre-heating.
Brush the top of your potpie with a pastry brush dipped in an egg wash made from one egg white and 1/2 cup of cold water.
Cover pot pie with aluminum foil and place on hot baking sheet in the oven. By placing your pie plate on the hot baking sheet you will help prevent the bottom crust from being soggy. It may also keep you from setting off your smoke alarm due to potpie filling oozing onto the bottom of your oven!
Bake for 45-50 minutes. Remove foil and continue baking until the filling starts to bubble up through the slits in the top crust and it becomes a beautiful golden brown!
Allow your pot pie to rest for about 10 minutes before you scoop into it.