A stretchy, easy cast-off that leaves an attractive edge.
Preparation: Cut the working yarn leaving a tail three times the length of the item you wish to cast off. Thread your yarn tail into a yarn needle.
Step 1: Working right to left, pass needle through the front leg of two stitches, as if to purl:
Pull the yarn through and make it snug, but not tight.
Step 2: Working back to the right, pass the needle through the front leg of the first stitch as if to knit. Pull the yarn snug.
Step 3: Slip the rightmost stitch off the needle.
Repeat steps 1 – 3 until all stitches are cast off. When working in the round, I just close the gap by inserting the sewing needle into the work at the beginning of the round as in step one, then back into the work from the front, and weave in the end.