When I was hunting for my last pattern for a pair of knit mittens, I wanted a pair of convertibles rather than straight up mittens or fingerless mittens. Unfortunately, I couldn't find any I liked... This is how I solved my pattern problem.
A pair of knit fingerless mittens (this time, I made "Owlings
", by Kerrie James - the link will take you to it's Ravelry page)
A ball of the same or co-ordinating yarn
Appropriately sized double pointed needles (4)
A large eyed sewing/darning needle
You may also choose to attach a button to each mitten, to hold the flip-top in place.
Having taken a look at the Owlings pattern online, it appears that it is currently unavailable for download - you need to contact the designer for the pattern. Any simple fingerless mitten will work, although, for this particular set of instructions, I'd suggest something in a DK/light Aran (worsted) weight yarn, based on around 40 stitches CO. A simple but effective pattern would be something like Fetching,
Ready? Off we go...