(Read Part 1 and Part 2 first.)
Now comes the fun part. And naturally, I'm missing some pictures. I think I can describe it okay, though.
Now you want to make sure the base of the fascinator is very smooth before you add the fabric and finishing touches. For this you use something called mull. It's basically an interfacing. You can order millinery mull, or you can use something from your stash. I used a little bit of very lightweight flannel. The flannel also gave the final product a little bit of definition. I covered the top, sewed it on with a whip stitch, then covered it with velvet, Here I've measured and trimmed the velvet, and tacked it on using a whipstitch.
I swirled a bit of craft grosgrain ribbon and stitched it to the velvet: