love hardanger designs myself, have played with this on embird, very intricate, but so worth it !!
Not lessons, but I have a lovely older set of designs called Heritage Hardanger from OESD (Oklahoma Embroidery Supply). I can pull a design into my digitizing software (Floriani Total Control Universe) and do a slow redraw and watch it stitch by stitch. This is one of the best ways to understand how well digitized designs are structured. Good luck with your project!
If you have digitising software including cross stitch there are stitch options in that which look like Hardanger. I did this example using Embird. I don't think lessons would be needed if you know what Hardanger looks like and have the software.
oh , this is gorgeous xx,