What You'll Need
Binding or Grosgrain Ribbon
Using the pattern you made back here, cut your fabric as indicated, and fuse your hat and one of your brim pieces with interfacing. You will have something like this:
With right sides facing, sew the outer edge of your brims together, at 1/4". Clip your seam allowance as shown below (this makes for a nice smooth edge once you flip it right-side out).
Flip right-side out and give a good press.
Fold your hat piece in half and sew at 1/2" to make a cone.
Clip your seam allowance to taper off at the pinnacle to avoid Lumpy Point Syndrome.
Flip right side out. Set your cone into your brim, pin and sew the cone to only the top layer of the brim.
Pin and sew your binding or grosgrain ribbon around the inside of the bottom layer of your brim.
At this point, if you so desire, insert a ring of wire into your brim. It should sit inside the very outer edge of the brim, and will keep your brim from flopping.
Clip the seam allowance behind the binding, so that it has room to stretch. Pin the upper edge of your binding to the inside of the cone and sew with a blind hem stitch.