Select parts from two loins containing ribs, scrape flesh from bone between ribs, as far as lean meat, and trim off backbone. Shape each piece in a semicircle, having ribs outside, and sew pieces together to form a crown. Trim ends of bones evenly, care being taken that they are not left too long, and wrap each bone in a thin strip of fat salt pork to prevent bone from burning. Roast one and one-fourth hours, covering bones with buttered paper. Remove pork from bones before serving, and fill center with Purée of Chestnuts.