Preheat the oven to 400 degrees.
Spray a nine-inch pie pan lightly with cooking spray.
Place the chicken broth in a small saucepan over medium heat.
In a small bowl, combine the three tablespoons of cornstarch with ¼ cup of water.
Stir with a fork until all the lumps are dissolved.
Stir this mixture into the warming chicken broth using a whisk.
Add ½ teaspoon of the salt, the pepper, the onion powder, the parsley, and the garlic powder.
Heat to boiling over medium heat, stirring frequently with a wire whisk.
When the mixture boils, lower the heat to simmer and cook about three to five minutes or until the gravy is thick.
Remove from heat, stir in the sour cream, and set the gravy aside.
In a medium-sized bowl, mix the flour and 1 teaspoon of salt with a fork.
Cut the stick of butter into small bits and add to the dry mixture.
Using a pastry blender, cut the butter into the dry ingredients until it resembles cornmeal, with tiny bits of butter scattered throughout the flour.
Add about a cup of ice-cold water, stirring with a fork, just until the dough comes together. Be gentle and do not overwork the dough.
Lightly flour your workspace and take half of the dough, lightly rolling it in the flour to coat it.
Shape the dough into a disk and using a rolling pin, roll it out into a 12-inch circle.
Lightly fold the crust into quarters and place it into the pan.
Unfold it to cover the bottom of the pie pan.
Shred the cooked chicken into the bottom crust.
Add the mixed veggies.
Pour the gravy over all of the veggies and meat, gently stirring to coat them.
Roll out the other half of the pie crust to a circle that is about 10 inches in diameter.
Place it over the top of the pie, covering the filling.
Crimp the edges and cut several vent holes into the top crust.
Bake the pie for 45 minutes to an hour.
If the edges of the pie begin to brown too quickly, cover them with strips of aluminum foil or a pie shield.
Let the pie cool for about 20 minutes before spooning your servings into bowls for serving.
Store leftovers tightly covered with aluminum foil in the refrigerator.
To reheat, you can place the whole pie pan back into the oven heated to 350 degrees for about 20 to 30 minutes.