If you want a finished edge, do the Eleanor Burns thing and cut a piece of lightweight fusible web larger than the Dresden Plate unit. Lay the web bumpy side up on your table and center the Dresden Plate unit on top, right side down. Pin to secure and stitch all the way around. Trim the edge to within 1/8" and then cut a slit in the middle of the back of the web and turn right side out, shaping the points for each one. Fuse the Dresden Plate unit to your background square.
You now have a finished edge which you can stitch down with a straight, zig-zag, button hole or blind hem stitch, by machine or by hand.