I cut out some 5″ circles (you could do any size) with my Go Baby! cutter, then sliced them in half with my rotary cutter and ruler.
Then sew two pieces right sides together, around the curved edge, I kept my seam allowance small, between 1/4″ and 1/8″, mainly so I wouldn’t have to clip the curves.
Turn right side out, and press.
Next I sandwiched the raw edge between some twill tape (bias tape would work too, I just had this in the right color), and pinned it together. Sew along the edge of the tape and you’re done!