Updated July 3, 2021.
I first learned this method of starting threads from Shay Pendray. It’s used widely in Japanese embroidery because it is economical on threads (important with expensive silks), easy, and invisible under most non-Tent Stitches.
Recently on a project I was worried about running out of threads and used this for all my starts. It was great and did a wonderful job of conserving my thread.
I highly recommend it.