1Preheat oven to 350 degrees. Melt butter in saucepan and cook chopped onion until tender. Stir in celery and carrots and cook for 2 minutes.
2Whisk in flour and cook for 2 minutes. Add chicken stock and half and half and bring to a simmer. Add potatoes and simmer until tender. Stir in chicken, parsley and peas.
3Pour mixture into casserole dish. Top with pie crust and brush with egg. Bake for 30 minutes until crust is golden.
Note: Depending on the casserole dish you use, you may have to roll the pie crust to fit. If you use a round dish, the crust should fit over top. If you use a square or rectangular, you will have to use two or roll it to fit.