In a large skillet, melt the butter over medium heat. Once melted, add the flour and stir for about a minute to create a roux. Gradually whisk in the chicken broth and milk, stirring continuously until the mixture is smooth and begins to thicken.
Add the dried thyme, onion powder, garlic powder, salt, and pepper to the sauce. Stir well to combine the flavors.
Fold in the shredded chicken and frozen mixed vegetables. Cook for an additional 5 minutes until everything is heated through. Remove from heat and let it cool slightly.
Preheat your oven to 425°F (220°C). Roll out one pie crust and place it in the bottom of your pie dish. Pour the chicken and vegetable filling into the crust. Top with the second pie crust and crimp the edges to seal. Cut a few slits in the top crust to allow steam to escape.
Bake the pot pie in the preheated oven for 25-30 minutes, or until the crust is golden brown. If the edges brown too quickly, cover them with foil.
Let the pot pie cool for about 10 minutes before slicing. Serve warm and enjoy!