I devised this pattern after practicing the 6 row cable stitch as found on http://eknittingstitches.com/simple-cable-stitch/

You’ll need multiples of 7 + 3sts. Adjust accordingly if you want to make a larger pair.

For S/M
Cast on 38 sts using the cable cast on.
Work 6 row repeat 7 times.
Bind off. You now have a cabled swatch.
Fold the swatch wrong-side facing out, and use a tapestry needle to stitch up the sides while leaving room for your thumb. Once finished, turn the handwarmers right-side out.

Repeat for the second handwarmer.

I decided I wanted a left leaning cable on my left hand, and a right leaning cable on my right. Instead of pulling the sts forward on the 5th row cable needle as the example shows, you’ll pull it behind the work to get the right leaning cable.