Preheat oven to 425° and roll out pie crust to fit a 9 inch deep dish pie plate. Place in pie plate and set aside (will need to roll out the top crust after filling is added).
Using a large frying pan or skillet, melt butter. Add onions and celery. Saute until tender.
Add turkey into pan. Add garlic salt and pepper. Stir to combine.
Sprinkle flour over turkey mixture and cook for 2 minutes.
Next, pour broth and heavy cream gradually into pan, stirring until combined. Continue to stir frequently until thickened.
Add mixed vegetables and cheese into turkey mixture Stir and cook for 5 minutes.
Spoon mixture into prepared pie crust.
Seal and fluke edges of pie and cut several slits into the top crust.
Make egg wash and brush top of pie crust.
Place pot pie plate on a baking sheet and bake for 35-40 minutes or until crust is golden.
*Place foil over edges of crust if the edges are getting too brown.
Remove from oven. Serve hot and enjoy.