How to prepare chicken breasts: Season chicken with basil, salt and black pepper. Bake at 350°F for 25-30 minutes or until internal temperature reaches 160°F. Let cool. When cool enough to handle, chop. Set aside.
Prepare pie crust using THIS recipe. Make two copies of the recipe. Cover the pie crust and let it cool in the refrigerator while you prepare your filling.
Preheat oven to 375°F Butter a 9x13 inch baking dish.
Over medium heat, melt butter in a large stockpot. Sauté onions until translucent, approximately 3 minutes.
Mix flour with water and stir. Cook the mixture for 2 minutes more.
Slowly add 1/4 cup of chicken broth at a time. Stir constantly. Slowly adding the broth will ensure that there are no lumps.
Stir in the milk. Cook on medium heat until the sauce thickens. To ensure that the sauce doesn't burn, you should stir it often.
Once the sauce has thickened to the consistency a medium-thick gravy add chicken, mixed veggies, basil, garlic powder and salt. Stir. Remove from heat and let cool.
On a lightly floured surface, roll out half of the pie crust. Place it in a greased 9x13 inch baking dish. Pour in sauce mixture. Spread the remaining pie crust on the top.
The excess pie dough should be removed. I press the top and bottom crusts together using a fork. To let steam and heat escape, cut slits into the top.
Use a pastry brush to brush egg-beaten over the top of pot pie
Bake at 375°F for 30 minutes. Cover and bake for 30 minutes. Then return to the oven and cook for another 30-35 minutes or until both crusts turn golden.
Take out of the oven and let cool for approximately 15-30 minutes before serving.