Preheat the oven to 425°F, and line a baking sheet with aluminum foil. Set aside.
Heat a large pan or Dutch oven over low-medium heat. Add the butter, onion, carrots, and celery. Cook for 5-7 minutes or until the vegetables begin to soften. Add the garlic, and cook for an additional 30 seconds just until fragrant.
5 tablespoons unsalted butter, 1 cup white onion, 1 cup carrots, ½ cup celery, 2 garlic cloves
Sprinkle in the flour, and cook for 2-3 minutes. Then, pour in the chicken broth and heavy cream. Increase the heat to medium, and stir to remove any lumps.
⅓ cup all-purpose flour, 2 cups low-sodium chicken broth, ½ cup heavy cream
Add the salt, garlic powder, dried thyme, and pepper. Continue cooking until the liquid begins to resemble a thick sauce.
2 teaspoons salt, ½ teaspoon garlic powder, ½ teaspoon thyme, ¼ teaspoon ground black pepper
Stir in the chicken and frozen peas until combined. Remove from heat, and set aside.
4 cups chicken, 12 ounces peas
Prepare one of the pie crusts by rolling it out onto a lightly floured surface, then transferring it to an ungreased 9-inch deep dish pie plate. The crust should be around 12 inches in diameter.
2 pie crusts
Carefully scoop the filling into the crust. Roll out the second pie crust to about 10 inches in diameter, and lay it over the top of the filling. Fold the excess dough from the bottom crust up over the top crust and crimp shut. Use a sharp knife to cut slits in the top crust.
Make an egg wash by whisking together the egg and 1 tablespoon of water. Use a pastry brush to apply the egg wash to the pie crust.
1 large egg, 1 tablespoon water
Transfer the pot pie to the prepared baking sheet, and bake for 30-35 minutes or until the top is golden brown. If the pot pie begins to brown too quickly, cover it with a foil tent.
Allow the pot pie to cool for 15-20 minutes before serving. See post for storage options.