If you need to know hot to make a sewn hem (picot or not), like in Pirouette, follow the instructions below.
Instructions
Cut the working yarn leaving a tail three times the length of the seam and thread it onto the darning needle.
Working from right to left, pass the needle up through the live stitch from back to front (1) and up through the purl bump of the stitch on the inside of the cardigan that it lines up with (2). Then pass the needle down through the purl bump of the stitch to the left of the one you just worked through (3), then through the live stitch once more from front to back (4). Drop this live stitch off your needle.
Repeat this motion through the next stitches to the left.
Repeat this all the way along the hem.
Weave in ends.
Video
You can watch a video of this technique here: https://pin.it/6u580Ch