Looked like to me on the Missouri Star Quilt Company tutorial she just kind of tacked it on by hand and then you could FMQ it down to hold it better. I plan to make one, someday and I do hand applique and hand sew on bindings, that is all the hand stitching I do anymore. Wouldn't be too hard to sew around the center with a straight stitch, if you did it before putting the squares together. What I plan to do it anyway.