Answer:
I wasn’t sure whether you meant rosette as in the cute little fabric flowers, or rosette as in th type with the ribbons, often given out as prizes, so I’ve found tutorials for both! Haha, I hope one of them is correct :)
These are the flower tutorials:
http://www.craftaholicsanonymous.net/2011/07/fabric-rosettes-tutorial.html
http://www.susieharrisblog.com/2009/11/diy-fabric-rosettes-and-more.html
and this one is for the prize-type rosette!:
http://www.ehow.co.uk/how_8690673_make-satin-rosette.html
I hope one of these works for you :)! If not, get back in touch and I’ll try and find you some more :)