In a large saucepan over medium high heat, combine the chicken breasts, thighs, chicken broth, salt and pepper. Bring to a boil and reduce heat to low. Cover and let simmer for 30 min., or until chicken is no longer pink in the center and the juices run clear.
Remove the chicken and let cool. Pour remaining chicken broth mixture into a measuring cup. Let stand; spoon off fat. Add enough canned broth to equal 1 cup if needed. Add half & half to the broth to equal 2 1/2 cups. Cut chicken into 1/2 inch pieces.
In same pan, melt margarine over medium heat. Add the onion & celery. Sauté, stirring, for 3 min. Stir in flour until well blended. Gradually stir in broth mixture and the herbs. Simmer, stirring constantly, until the sauce thickens & boils. (you will think this is TOO MUCH liquid, but it's not. Add the chicken & vegetables to the broth & stir to combine. Line a deep pie dish with one of the pastries & pour mixture in, almost to the top.
cover mixture with 2nd pastry - seal edges pinching together - cut vents or prick with a fork - brush the top with egg.
Bake at 400 degrees for 30 minutes or until the crust is golden brown & the filling is bubbling. Let cool for 10 minutes and serve.
When done, the inside ingredients will be thick and creamy.