Sorunda 2 Stitch (Finnish Stitch 1+3½)

F1 or F2 (Anderson's book doesn't specify) 

Hansen's Notation
UOOOo/uUUUOO F1  (video)
small o and u = yarn is split with the needle (ie needle in between the plies)

One loop around thumb, three loops behind the thumb, and 4th loop is split.