1. Prepare Oven and Pie Dish:

• Preheat the oven to 425°F (220°C).
• Have your 9-inch deep-dish pie pan ready. (No need to grease if using standard pie pastry, but follow pastry package if it suggests it).
• Place a baking sheet in the oven while it preheats (this will help crisp the bottom crust).

2. Make the Creamy Chicken Filling:

• Melt the ⅓ cup of butter in a large skillet or saucepan over medium heat.
• Add the ⅓ cup of chopped onion and cook, stirring occasionally, until the onion is translucent and softened, about 5 minutes.
• Sprinkle the ⅓ cup of all-purpose flour, ½ teaspoon salt, and ¼ teaspoon pepper over the cooked onions. Stir constantly and cook for 1-2 minutes to create a roux and cook out the raw flour taste.
• Gradually pour in the 1 ¾ cups chicken broth and ⅔ cup milk, whisking constantly to prevent lumps.
• Bring the mixture to a boil, stirring frequently. Continue to cook and stir for about 1 minute, or until the sauce has slightly thickened.
• Remove the skillet from the heat. Stir in the 2 cups of chopped cooked chicken, the drained can of peas and carrots, and the drained and quartered/diced canned new potatoes until everything is well combined in the creamy sauce.

3. Assemble the Pie:

• Ensure your pie pastry is thawed according to package directions.
• Carefully unroll one pie pastry and press it into the bottom and up the sides of your 9-inch deep-dish pie pan. Trim any excess if needed, but leave a slight overhang.
• Pour the prepared creamy chicken and vegetable mixture evenly into the pastry-lined pie pan.
• Unroll the second pie pastry and place it over the top of the filling.
• Seal and Vent: Trim the excess pastry from the top crust, leaving about a ½ to 1-inch overhang. Fold the edge of the top crust under the edge of the bottom crust, then press them together firmly to seal. Crimp the edges decoratively with your fingers or a fork.
• Using a sharp knife, cut several small slits (vents) in the center of the top pastry crust to allow steam to escape during baking.

4. Bake the Pot Pie:

• Carefully place the assembled pie onto the preheated baking sheet in the oven.
• Bake for 30 minutes, or until the crust is beautifully golden brown and the filling is bubbly (you might see some bubbling through the vents).
• If the crust edges start to brown too quickly before the pie is done, you can loosely shield them with strips of aluminum foil or a pie crust shield.

5. Cool Slightly and Serve:

• Let the baked Chicken Pot Pie cool on a wire rack at room temperature for at least 15 to 20 minutes before slicing and serving. This is very important, as it allows the hot, bubbly filling to thicken and set up properly; cutting into it too soon will result in a very runny filling.
• Slice into wedges and serve warm. Garnish with fresh parsley if desired. Enjoy this comforting classic!