Heat butter over low heat until melted. Blend in flour, onion salt, poultry seasoning, salt and pepper. Cook over low heat, stirring constantly, until mixture is smooth and bubbly; remove from heat. Stir in broth and milk. Heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in chicken and frozen vegetables.
Prepare pastry. Roll 2/3 of pastry into 13-inch square on lightly floured cloth-covered board. Ease pastry into square pan 9x9x2 inches; pour chicken filling into pastry-lined pan.
Roll remaining dough into 11-inch square; place over filling. Roll edges under; flute. Cut slits in center to allow steam to escape. Cook uncovered in 425 degree oven until crust is brown, 30-35 minutes.
Makes 6 servings.
