Clip one of the edge and turn this inside out.
Get your ruffler foot and make ruffles. I made mine: Stitches 6, depth 3. Set aside.
Get one of the back piece (plain in mine) and the zipper. Open the zipper all the way. Attach the zipper foot of your machine. Align the edges of the zipper and fabric, right sides together and sew straight stitches 1/4" away from the edge. Topstitch.
Repeat the same procedure with the other piece of fabric.
Using a compass, I drafted circles in a piece of paper. My spiral started from 0.5 to 2.5
I didn't have enough fabric to reach until 3.0
Get your iron-on or sew on interfacing and trace the circles you drafted with fabric pen. Iron on the interfacing on the center of the fabric or pin it to the fabric if you decided to use sew on interfacing.
Sew on the rufflesby sewing 1/4" away from the raw edge of the ruffled strip, using the circles on the interfacing as guide.
Keep on sewing...
Until you use up all of the ruffled fabric strip.
To avoid fraying, I sewed zigzag stitches on the ruffled spiral. Sew on an embellishment in the center, could be a pretty button, a handmade yo-yo, etc.
Get the back part of the pillow (with zippers) and the front piece with the sewn-on ruffles, pin both pieces right sides together. Leave the zipper open half-way. Sew straight stitches 1/4" away from the edge on all four sides of the pillow cover.
Clip all four tips and sew zigzag stitches on all sides to avoid fraying.
Turn the pillow cover inside out and enjoy it!