Combine beef, pork, bread stuffing, onion, salt, pepper, egg and mushroom gravy in large bowl; mix lightly with fork. Shape into roll about 10 inches long.
Prepare pie crust mix, following label directions. Roll out to a rectangle 16 inches by 10 inches on lightly floured board. Place meat in middle, fold pastry over meat, seal edges leaving ends open. Place seam side down in greased shallow pan; cut several slits in top of pastry to allow steam to escape.
Bake in hot oven, 475° for 15 minutes; reduce heat to slow, 325° and bake 1 hour longer until pastry is golden brown.
Cut in thick slices, and serve hot; also may be served chilled.
