i draw the circle on interfacing, put fabric right sides together, sew all the way around. carefully cut slit into interfacing in the center. turn right side out and use whatever tool you have to run around the seam line from the inside. i use the blunt end of a nut-picker, or you could use a crochet hook. then press the circle and then i sew it in place using regular stitching on my machine. you could hand sew also if you do not want stitching lines showing.