Heat butter over low heat until melted. Blend in flour, onion , salty and pepper. Cook over low heat, stirring constantly, until mixture is smooth and bubbly; remove fro heat. Stir in broth and milk . Heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in chicken and frozen vegetables; reserve.
Use 2/3 of the Celery Seed Pastry to line a 9x9x2 inch pan. Pour in the filling and top with the rest of the pastry.
Bake at 425° F. for 30 to 35 minutes or until crust is golden brown.