"My family loves this recipe. It's easy to do and you get a chicken pot pie that's way better than what you buy at the store. A complete, homemade meal in 1 pie dish. I normally cook up more chicken than I need. I then take the leftover chicken and stock and freeze it for use in something else later. As much as my family loves this recipe, the extra doesn't last long. I like to make a nice lettuce salad to go along with. Remember you can use whatever veggies you like whether they are frozen, fresh, or canned. It's always nice to fix this in the summer when you can get your veggies from the garden or the farmer's market, but canned and frozen work great too."
Place chicken in a stockpot and add just enough water to cover; stir in poultry seasoning, sage, garlic powder, salt, and black pepper. Bring chicken mixture to a boil, reduce heat to medium and simmer until chicken is no longer pink at the bone and the juices run clear, 30 to 60. An instant-read thermometer inserted into the thickest part of the thigh, near the bone should read 165 degrees F (74 degrees C).
Remove chicken from cooking liquid; reserve cooking liquid, remove and discard bones and skin from chicken and dice chicken meat.
Preheat oven to 375 degrees F (190 degrees C). Spray a pie plate with cooking spray and line it with 1 of the prepared pie pastries.
Stir diced chicken meat, potatoes, onion, carrots, and mixed vegetables together in a bowl. Pour chicken mixture into prepared pie plate.
Bring 1 cup reserved cooking liquid to a boil in a saucepan. Whisk cornstarch into cooking liquid and cook, whisking constantly, until gravy thickens, 3 to 5 minutes. Season gravy with salt and black pepper. Pour gravy over chicken mixture into prepared pie plate. Spread remaining pie pastry over the top, crimp edges together, and cut a slit in the top of the pie.
Bake in the preheated oven until heated through and crust is golden, about 1 hour. Cool for 5 to 10 minutes before slicing.