they are made with thin strips of fondant/gumpaste coiled and folded at your whim against a fondant covered cake. There are a few tutorials out there on YouTube that show the technique.
I am almost positive that Craftsy has a class on this.
AHello...Vivalacake blog...have an excellent tutorial. If u dont find her blog let me know. Good luck
Crsftsy has a class on ruffles but not this sort.