Preheat oven to 375˚
Heat a sauce pan over medium heat, add in chicken breasts, chicken broth, salt and pepper. Bring the broth to a boil, cover and allow to simmer for 30 minutes. Remove chicken from and allow to cool.
Pour remaining broth, add in your half and half mix together and set aside. Cut chicken into small 1/2 inch chunks.
Melt butter in pan, once melted add in the celery and onion. Stir constantly for about 3 minutes allowing them to get tender.
Slowly whisk in he flour until completely blended, after about a minute slowly add in the the broth mixture whisking until completely combined. Add in the rest of the seasonings. Constantly stir until it begins to thicken. Add in the chicken and vegetables allow to simmer.
Line a pie pan, or oven safe skillet with one of the pastries. Pour in the the chicken filling and cover with the second pastry, pinching the edges of the two pastries together. Slit holes in the top and brush with the egg.
Bake for 30-35 minutes, until the crust is a golden brown.