In a small skillet melt 2 Tablespoons butter. Add in 3/4 cup chopped celery and 1/2 cup diced onion. Saute till translucent.
In a large bowl add 4 cups chopped chicken, sauteed celery and onions, diced cold potatoes, 3 cups of frozen mixed vegetables, salt, pepper, thyme, oregano, sage, garlic salt and fresh parsley. Mix.
Add in 1 can cream of chicken soup and the 18 oz. jar of chicken gravy. Mix till well blended.
Roll bottom pie crust out. Place in deep pie plate.
Fill with meat and vegetable filling. Spread out evenly with slightly mounded center.
Roll out top pie crust. Gently place on top of filling. Trim around outside edge of pie plate. Fold excess crust under. Flute crust edges with fingers. Cut small slits for vents in the top of the crust.
Beat egg with water. Using a pastry brush, brush top of crust with egg wash.
Place pot pie on top of foil lined baking sheet.
Place in preheated 325° oven and bake for 45-55 minutes.
Pie is done with golden brown and filling is bubbly. (If crust begins to brown to soon cover with foil tent.)
Allow to cool for 10 minutes. Slice and serve.