Description from Knitty.com:
Fair-isle mittens, afterthought thumb. Sounds simple but there are many ways to jazz up these mittens. They can be knit from the cuff-to-top, in the normal way, or from the top-to-cuff for a bit of fun (guidelines for a top-down mitten are given as a variation at the end of the pattern). One great advantage to the latter method is that you can make the cuffs almost as long as you want without worrying that you'll run out of yarn later.