Just a simple, no frills, two hour project.

CO 40 sts
Knit in 3x1 rib for 9cm.

Increase method: the first 12 sts are the thumb section, add before and after thumb section every other row for 8 rows (8sts added) - M1R - 12 in pattern - M1L; next increase row add before and after added sts.

Knit in pattern another 5 cm.
Put 12 thumb sts on holder.

Knit in pattern another 3-4 cm.
Bind off in pattern.

Use the 12 sts for thumb, pick up and knit 2 sts in the round from the main section --> thumb 14 sts. Knit the thumb in pattern for about 1.5 cm. Bind off in pattern.

Make another mitt.