Cook chicken and onion in butter in a large skillet over medium high heat, stirring until chicken is browned and onion is tender.
Stir in celery and the next 8 ingredients. Bring to a boil, cover and reduce heat. Simmer 15 minutes or until vegetables are tender. Discard the bay leaf.
Combine cornstarch and 2 tablespoons of water, stirring until smooth. Add to chicken and celery mixture. Bring to a boil over medium heat, stirring constantly. Remove from heat, stir in soup, cheese and sour cream.
Roll half of pot pie pastry and fit into an ungreased pie pan or casserole dish. Spoon chicken mixture into the dish. Place remaining pastry over chicken mixture, trim, seal and crimp edges.
Cut slits into top of pastry. Combine egg yolk and 1 tbsp. milk; brush over pastry.
Bake at 400 degrees for 35 minutes or until golden. If the crust starts to brown too quickly, simply cover it with aluminum foil.
Serve hot and enjoy!
Notes
This comfort food recipe is out of this world amazing and is sure to impress!