What do you know? I did find a pattern for mittens that are knit flat ... apparently there are lots of them!
You could check out this one
if you like.
If you haven't already, I would definitely recommend checking out the videos page here on KH to learn how to increase/decrease and seam before you get started. These are all very easy, so don't worry .... but it's worth being prepared so you don't get too frustrated with your new project!