I found the easiest way to keep track of what I was doing was to use 2 circulars and a pair of DPNs (I would have used 3 circulars, but I didn't have 3 at the time). I separated the back of the hand, the palm of the hand and the thumb gusset onto their own needles. By using this method, it also makes it easy to adapt the pattern for left and right - just move the thumb stitches to one side or the other.
I hope my explanation works for you, but if you have any troubles please write in the comments and I'll get back to you as soon as I can.
For the right hand mitt, the needle order goes: back of hand, thumb, palm.
For the left hand mitt the needle order is: back of hand, palm, thumb.
Yarn: Once again I used Moda Vera Marvel 8ply yarn, simply because that's what I had with me at the time. Any 8ply/DK yarn should do the trick. I'm not very good at keeping track of how much yarn I used, but the finished gloves weigh 30g. Obviously you'll need more in your main colour than contrast colour.
Needles: 4mm. As mentioned above I used 2 circs and a pair of DPNs, but you could use all DPNs if you prefer. The magic loop would work, too, but you wouldn't be able to separate the thumb stitches.
Extras: yarn needle for weaving in ends and for threading the lace up. I used yarn for the lace up, but they would also look pretty with ribbon.
K = knit
P = purl
S1 K2tog PSSO = slip stitch knitwise, knit 2 stitches together, pass slipped stitch over
YO = yarn over
KFB = knit front and back of stitch
The eyelets are repeated every 4 rounds and once introduced the thumb gusset increases are every 5 rounds.
Cast on 38 sts using contrasting colour. I wanted to make sure it wasn't too tight so I cast on over 2 needles. Use your preferred stretchy cast on method. Distribute stitches evenly between two circular/DP needles. Work 5 rounds of K1P1 rib.
Rnd 6: change to main colour and knit all stitches
Rnd 7: Back needle K4 YO K4 S1 K2tog PSSO K4 YO K4; K remaining stitches
Rnds 8-10: K all
Rnd 11: as for Rnd 7
Rnds 12-14: K all
Rnd 15: as for Rnd 7
Rnd 16: K all
This is where the thumb gusset starts.
Rnd 17: K all stitches on first (back of hand) needle. For RH mitt move FIRST two stitches
and for LH mitt move LAST two stitches from the second (palm) needle to third (thumb) needle. KFB both stitches. There are now 4 stitches on thumb needle. Stitches on the palm needle are knitted also.
Rnd 18: K all
Rn 19: as for Rnd 7
Rnds 20-21: K all
Rnd 22: K all stitches on back & palm needles. KFB first and last stitch on thumb needle (now 6 stitches on needle)
Rnd 23: as for Rnd 7
Rnds 24-26: K all
Rnd 27: Back needle as for Rnd 7; Palm needle knit all; Thumb needle KFB first and last stitch (8 stitches on needle)
Rnds 28-30: K all
Rnd 31: as for Rnd 7
Rnd 32: as for Rnd 22 (10 stitches on needle)
Rnds 33-34: K all
Rnd 35: as for Rnd 7
Rnd 36: K all
Rnd 37: as for Rnd 22 (12 stitches on needle)
Rnd 38: K all
Rnd 39: as for Rnd 7
Rnds 40-41: K all
Rnd 42: as for Rnd 22 (14 stitches on needle)
Rnd 43: as for Rnd 7
The thumb stitches are now going to be held.
Rnd 44: K all stitches on back needle. It gets a bit fiddly here as only 12 stitches need to be held for the thumb. The first and last stitch are moved back to the palm needle on whatever side the thumb is and two stitches are cast on in between (I used the back loop method). All stitches on palm needle are knitted.
Rnds 45-46: K all (back and palm needles only)
Rnd 47: as for Rnd 7
Rnds 48-50: K all
Rnd 51: as for Rnd 7
Rnd 52: K all
Rnds 53-57: change back to contrasting colour & work in K1P1 rib.
Cast off using the Elizabeth Zimmerman sewn bind off (see Snail Spirals' pattern linked above for details).
Now to finish the thumb.
Redistribute the held stitches over 2 needles. Join contrasting colour yarn. Work 3 rounds in K1P1 rib. Cast off using the same method as above.
Once both gloves are finished, weave in all the ends and lace her up! I used 2 strands of the contrasting yarn. I have the ends woven in on the inside of the glove, but you could also tie them in a bow at the top or bottom of the glove.
If you make these, please link to them on Ravelry or post pictures in the comments - I'd love to see the different colour combinations that you all come up with.