Preheat oven to 375 degrees. Add 3 cups water to a saucepan. Add raw chicken breasts and 2 bouillon cubes. Bring to a boil and simmer for 20 minutes or until chicken is no longer pink in the middle.
Remove chicken breast from broth and cut into 1/2 inch cubes. Set aside.
In the same saucepan, add potatoes, carrots, corn, and peas to broth. Bring to a boil for 10-15 minutes or until potatoes are fork-tender. Remove from heat. Place a colander in a large bowl. Drain vegetables into colander and save the chicken broth in the bowl.
In a large pot over medium heat, sauté garlic, onions and celery in butter until soft and translucent. Stir in flour, salt, pepper, and celery seed. Slowly stir in 1 3/4 cups of remaining chicken broth (add water if there isn't quite enough broth for 1 3/4 cups) and milk.
Simmer over medium-low heat until thick (if you like a thinner sauce, add more chicken broth and milk a little at a time until you reach desired consistency). Gently stir in the cooked vegetables and cubed chicken to the sauce. Remove from heat and set aside.
Place one of the pie crusts in a 9” pie pan. Pour chicken and vegetable filling into the pie crust.
Lightly moisten the outside rim of the pie crust by dipping your finger in water and "painting" around the edge of the crust. This will help to seal in the juices so it doesn't make a mess in your oven.*
Place the top crust over the pie. Trim off any excess dough of the top crust that comes over the edge of the pie tin with a butter knife. Seal the top crust to the bottom crust by crimping the edge as shown.
Cut small slits in the top of the crust in a decorative pattern.
In a small bowl, whisk egg white until it is foamy. Using a pastry brush, brush the top of the pie with the egg white.
Bake for about 35-40 minutes or until the crust is golden brown.