They are beautiful!
I am not 100% sure how they were done, but here is my best guess.
Pipe the design onto the cookies, let them dry, paint them with a very thin layer of almost water-like icing and instantly cover with very fine sugar. Then add the details you don't want to sparkle.
I checked Kim's blog, but couldn't find a tutorial for it there, only a similar design which she made with fondant stripes. But it was much less delicate, so that is probably not what she did here.