Whipped blanket stitch
This stitch is formed of a line of blanket stitch with a thread whipped around the lower edge of the stitch. The whipped thread can be the same as the blanket stitch thread, or a contrasting one.
Introduce a new thread, coming up right next to the anchoring stitch at the end.
Work from right to left. Pass a tapestry needle under lower edge of each blanket stitch for whipping.
Structure of stitch
Jennifer Campbell, Ann-Marie Bakewell, Guide to Embroidery Stitches (2004) , p.122