Wanted approximately 25 inches in length.
Ch 85
Row 1: SC in back ridge of 2nd chain from hook and each chain across.
Row 2: Turn, Ch 1, Sl St in front loop only of each SC across.
Row 3: Turn, Ch 1, SC in free loops of each SC from the previous row across.
Repeat rows 2 & 3 for pattern to desired width.

I repeated the pattern rows a total of 25 times. At end of row 51: turn, Ch1, SC in each SC across, 3 SC in corner SC, rotate, SC in each row along short edge, 3 SC in corner, rotate, SC in each SC across to next corner, 3 SC in corner.

Because of the nature of the slip stitch, one short edge is a lot more loose and stretchy than the other. On that short edge, I did a decrease SC: insert, yo and pull up a loop, insert in next row, yo and pull up a loop, yo and pull through all 3 loops. Do that across that last short edge. 3 SC in corner. Working on same short edge side: turn, Ch1, SC in each SC across repeat 6 more times.

Continue the border around the whole thing again: Rotate, 1 round of SC around the entire cowl with 3 SC in corners. Sew buttons evenly across the short edge with the SC trim. Pull the short edge across to the end of each long edge (a bit like a mobius strip) and mark approximately where the buttons line up with a stitch marker. Doing this on both sides allows the wearer to wear the buttons on the right or left shoulder.

During the last round of SC: SC in each SC around, 3 SC in each corner. At the stitch markers: Ch 3, Skip 3 SC (the one before, the marked one, and the one after) for button holes, SC in next SC and around to next stitch marker, Ch 3, Skip 3 SC (the one before, the marked one, and the one after) for button holes, SC in next SC and around. Join to beginning of round with a slip stitch. Weave in ends.