Here's the way I did it. The first step is to prepare your willow strips, and then plait a rectangle the size of your foot.
Then I attached it to my foot mold (plaster) with rubber bands. (Yes, I did make a right and left mold.)
Weaving around the sole. I had to adjust the weave on both sides because this is the place the foot gets more narrow. I am using sisal twine here, but you can use any small cord.
Going around the heel area, you have to adjust by dropping some of the ends, and twine on an angle.
I finished off with a few more rows of the paper cord, and a folded down border. On the first shoe, I tried a cedar rose. After I made the left one, I decided they needed some bling.
As I started the left foot, the challenge quickly started. This one had a different count of willow pieces, and a totally different shape at the toe area. I wove it once, took it out, and wove it again. I realized that my 2 feet were very different, and that I would just have to live with them not matching perfectly.