You will need:
2.75mm circular needles (2.5mm for women's)
Approximately 50gm fingering weight yarn. (For these I used a long-deleted Shepherd brand 4-ply crepe, for his partner's I'm using Haven by Naturally - much, much softer than the crepe)
2 small safety pins to use as stitch holders
A stitch marker for thumb gusset increases.
Cast on 64 sts and join for working in the round (32 sts per needle).
Work in K2, P2 rib for 3 inches.
For the next 2 inches, knit in K1, P1 rib.
Next round: KFB, P1, *K1, P1 rib to end.
Next round: KFB, KFB, P1, *K1, P1 rib to end.
Next round: KFB, K1, KFB, PM, *K1, P1 rib to end.
Next round: KFB, K3, KFB, PM, *K1, P1 rib to end.
Next round: KFB, K5, KFB, PM, *K1, P1 rib to end.
Continue increasing 2 sts per round in this manner until you have 27 extra sts before the marker.
Next round: K 27 and put
half (ok, not an even number) 13 sts on one safety pin, and 14 on the other. forget about those sts for the meantime, and continue to K1, P1 rib for another 5 rounds. Make sure you snug those sts up in the beginning of the rounds so as to help close up any gaps between the thumb and the hand of the mitt.
Change back to K2, P2 ribbing for the final 2.5 inches (2 inches for women's), cast off (or bind off, whichever takes your fancy) knitwise.
Put those thumb gusset sts back onto your needles. On the needle with 13 sts, pick up an extra 2 sts from the hand section, and on the needle with 14 sts, pick up one extra stitch. Knit one round plain.
Next round: K2tog, K1, *P2, K2 to last 3 sts, P2tog, P1.
Continue in K2, P2 rib for 6 more rounds, cast off knitwise.
Work in your ends, using the end that you joined on at the thumb to close up any hole between the thumb and hand sections. Do it all over again for the 2nd mitt.
As per usual, use the pattern for whatever, but please link back to my blog and credit me as the designer. If anything is unclear or doesn't quite seem right, let me know and I'll fix it up.