Roll out the chilled homemade pie dough on a floured surface until it’s about 1/8 inch thick. Carefully fit the dough into a 9-inch pie dish, letting the edges hang over. Trim any excess dough.

In a medium pot, bring salted water to a boil and add the boneless skinless chicken breasts. Cook for about 15-20 minutes. Remove from the pot and let cool before shredding into bite-sized pieces.

In a large skillet over medium heat, melt 1/3 cup of butter. Add sliced celery and chopped onion and sauté for about 5 minutes.

Stir in all-purpose flour, salt, black pepper, celery seed, and garlic powder, ensuring everything is well combined.

Gradually pour in milk while stirring continuously. Add chicken bouillon paste and bring the mixture to a gentle simmer for about 3-5 minutes until thickened.

Fold in shredded chicken and frozen mixed vegetables, stirring until well incorporated.

Allow the filling to cool for about 10 minutes, then pour it into the prepared pie crust. Roll out reserved dough for the top crust and place it over the filling.

Seal the edges by pressing them together and cut a few slits in the top crust. Preheat your oven to 375°F (190°C) and brush the top with egg wash.

Bake for 30-40 minutes, or until the crust is golden and the filling is bubbling. Let cool for about 10 minutes before serving.