From the Knit Picks Website:
They say “Diamonds are a girl’s best friend.” That phrase is the inspiration for this pattern. These fingerless mitts are knit flat and seamed up the edge, because I wanted to use the tubular cast-on, which must be worked flat. You could use the standard long-tail cast-on, if you prefer. I like the tubular cast-on because it is more stretchy than other cast-on methods. Likewise, a standard (loose) bind-off can be used if you prefer that to the sewn bind-off. There are two sizes, one for girls, which easily fit my 5 and 9 year old daughters, and one for women which should fit an average size woman.

Tubular cast-on recommended.

See also A Girl’s Best Friend Scarf