Portuguese knotted stem stitch
This stitch is not actually a knotted stitch. However it visually gives the impression of a knotted version of stem stitch and it creates a textured, rope-like line when stitched with a thick twisted thread.
Start by working a stem stitch. After bringing up a needle halfway, slide the needle under the first stitch. Do not go through the fabric.
Pull the thread tight to wrap the stem stitch, and then slide the needle under the first stitch again. The second wrap sits just below the first wrap.
Keep the loop to the right of the needle and come up in the same hole at the end of the first stem stitch.
Work another wrap so that it lies in place below the first wrap. Make sure not to pick up the fabric when whipping.
Structure of stitch
Mary Thomas, Mary Thomas’s Dictionary of Embroidery Stitches (1934) , p.15
Kate Haxell, The Stitch Bible (2012) , p.102
Jennifer Campbell, Ann-Marie Bakewell, Guide to Embroidery Stitches (2004) , p.49
Erica Wilson, Erica Wilson’s Embroidery Book (1975) , p.37