Bind-off with a 3rd needle

Take an additional needle-tip a half size lager as your working needles, and make a twisted loop with the working yarn.

Slip the first stitch on the front needle as if to knit.

Purl the first stitch on the back needle.

Pass the second and third stitch on the bind-off needle over the first stitch. Go to image 2 again.

This creates a pretty “seam”, which is much flatter than the conventional “3-needle bind-off”.