As to how I've done it, I considered curved piecing I am comfortable w/ that but thought it would be so much more accurate and easy to just machine applique. So I made a brown paper (think paper sack) template put a tiny touch of stick glue to hold it in place, trim the edges of the fabric to 1/4 ish inch from the curve clip edges press under w/ a hot iron, let cool, take paper off, use a little more glue w/ a hot iron to make sure pressed under seam stays put place on the background sashing fabric and machine straight stitch the folded edge.