Sauté onion in butter until tender. Add meat; cook 5 minutes. Sprinkle flour over meat, stirring constantly. Gradually add broth; cook over medium heat, stirring constantly, until thickened. Stir in next 8 ingredients. Spoon mixture into a 9- inch pie plate.
Roll pastry to 1/8-inch thickness on a lightly floured surface. Carefully place pastry over beef mixture. Turn pastry edges under, and press firmly to rim of pie plate to seal; flute edges. Cut slits in top to allow steam to escape. Decorate with pastry cutouts, if desired. Brush top with beaten egg. Bake at 350° for 45 minutes or until golden brown.