Finnish Stitch 1+1½  (Valö Stitch)

Hansen's Notation 
UOo/uUOO F1  (video)
small o/u = split the yarn with needle   

Finnish Stitch 1+1½, front side
Valö Stitch
F2 (on the left) - F1 (on the right) 
Finnish Stitch 1+1½, reverse side
Valö Stitch
F1 (on the left) - F2 (on the right)

In Rothquist Ericsson's book this stitch is from Valö (Uppland, Sweden).

1 thumb loop, 1 loop onto needle, 2nd loop behind the thumb is split with the needle (ie push needle in between the plies). Finish off as usually.