In a large bowl, beat eggs, add milk, saltines, apple and onion. Add the sausage and mix well. Lightly press into a greased 6-cup ring mold or other mold. Invert onto a lightly greased 15x10x1-in. baking pan; remove mold. Bake, uncovered, at 350° for 1 hour or until a thermometer reads 170°; drain.