More than a button but less than a kilt.
I would start with some thread, Knot the end about 3-4 knots. Bring it up thru the pleat you want to join, the one to the right. Then thru the pleat that you want to join to the left. Then use a hiddien stitch up to where the trhread is broken and then past to make sure you are locking in the machine thread.
Easy huh?