Fill a pot with salted water and bring it to a gentle boil. Carefully add the boneless skinless chicken breasts and poach for 12-15 minutes until fully cooked. Remove and shred it, reserving about 1¾ cups of the cooking liquid.

In a medium saucepan, melt ⅓ cup of unsalted butter over medium heat. Add the finely diced onion and diced celery, sautéing for 4-5 minutes until soft. Gradually stir in ⅓ cup of all-purpose flour and cook for 1-2 minutes until light golden, forming your roux.

Add ½ teaspoon of garlic powder, ¼ teaspoon of celery seed, ¼ teaspoon of black pepper, and 1 teaspoon of chicken bouillon paste to the roux. Stir well and let it cook for an additional minute.

Slowly whisk in the reserved cooking liquid and 1 cup of whole milk to the roux. Stir for 3-4 minutes until thickened, then fold in the shredded chicken and frozen mixed vegetables.

Allow the filling to cool for 15-20 minutes. Preheat your oven to 425°F.

Roll out your pie dough and place one crust in the bottom of the pan. Spoon the cooled chicken mixture evenly into the crust.

Roll out the second pie dough for the top crust. Seal the edges and cut a few slits for steam vents.

Brush the crust with an egg wash made from 1 egg and 1 tablespoon of milk. Place on a baking sheet and bake for 40-50 minutes until golden brown and bubbly.

Let the pot pie rest for 15-20 minutes before serving.