I use a similar method to this when I do a "Drunkards Path", I cut a circle in cardboard then cut a circle in the fabric slightly larger than the cardboard , sew gathering stitches around the edge of the fabric about 1/4 inch in, place over cardboard pull gathering stitches press to the inside, carefully remove cardboard then you have a circle of fabric, cut into four and use it for a drunkards path, top stitch the half circle to your background fabric or neatly hand stitch. Somewhere in the archives on this quilting board is my quilt called "Circle of Crowns" which was done this way for your reference.