Separate ribs into single pieces. In a large bowl, mix together soy sauce, sherry, scallion, ginger, and black beans. Add ribs and toss to coat well. Cover and refrigerate 30 minutes. Coat a 9" heatproof plate with oil. In a shalow bowl mix cornstarch, five spice powder, and salt. Toss ribs in seasoned cornstarch to coat and place on oiled plate. Place in a bamboo steamer. Pour any remaining marinade over ribs. Cover and steam 45 minutes, until ribs are tender.