Since I didn’t use a pattern, here’s my “recipe”:

Cast on 20 with CC and knit 3 rows.
Change to MC and knit 1 row (rnd 1).
Join to knit in round, and knit in the round, increasing for thumb on rnds 3, 5, and 7.
On round 9, place 7 sts on holder for thumb, cast on 1 st, and continue knitting to a total of 18 rnds.
Decrease 4 sts every other round, until 8 sts remain.
Cut yarn and draw end through all sts, securing at the inside of the mitten.
Place 7 thumb sts on needle, and pick up 2 or 3 additional sts. Decrease to 8 sts on round 2.
Knit 5 rnds + 1 decrease round, then cut yarn and draw end through all sts, securing at the inside of thumb.
Stitch up CC at thumb side, and crochet loop for hanging.