Preheat oven to 425 degrees F. Season chicken with salt and pepper. Add the chicken to a large saucepan and cover it with water. Bring to a boil and cook for 6-10 minutes or until the chicken is just barely cooked through. Remove the chicken to a plate, reserve about 1 3/4 cups of the water in a measuring cup, and discard the rest.
Add onions, celery and butter to the saucepan and cook for a few minutes, until soft and translucent. Stir in the flour, salt, pepper, garlic powder, bullion paste and celery seed.
Slowly stir in the reserved water and milk. Simmer over medium-low heat until thick.
Chop the chicken and add it to the pot along with the frozen vegetables. Taste and season with more salt, pepper, bullion or garlic powder if needed.
Pour mixture into bottom pie crust. Cover with top crust, seal edges, and cut away excess dough. Make a few small slits in the top crust to allow steam to escape.
Bake for 30- 35 minutes, or until pastry is golden brown and filling is bubbly. If you find the pie crust is browning too quickly, cover it with tinfoil. Cool for at least 15-20 minutes before serving to allow it to set up.
*Nutritional information does not include pie crust. (calories vary for homemade or store-bought crusts).Recipe adapted from All Recipes