Chicken Pot Pie

1 rotisserie chicken or canned chicken
1/2 large onion, diced
2 stalks celery, diced
10 small mushrooms, halved
4 T butter or oil
1/4 c flour
1 pint 1/2 and 1/2
1 cup chicken broth
1 bag frozen mixed vegetables
1 box frozen pie crust

Pull meat off bone and set aside. Saute onion and celery in 2 T butter until tender. Stir in flour and cook 3-4 minutes. Stir in half and half until thickened. Stir in enough chicken broth to make a consistency of creamed soup. Stir in mixed veggies. Heat through and seasoning to taste. Stir in chicken and mushrooms. Place mixture in pie crust and bake at 375 for 40-50 minutes. Let sit 15 minutes before serving.