This is one of the embellishment techniques I was demonstrating at the quilt show last weekend. It is very easy, and quick to do. All you need is a length of wide lace trim, sewing thread and needle. I include several cuts of dyed lace trim in my Creativity Kits, available on my Etsy shop.
1. Cut a length of lace trim, 7" to 12" long, cut a length of matching thread, thread your needle and knot.
2. Fold 1/4" of short end of lace to the backside, bring needle up through fold. Sew a long running stitch along the long flat side of your lace trim, as close to the edge as is reasonable. Be sure to catch the thread in the thicker parts of the lace.
3. When you reach the other short end of the lace, fold 1/4' of the end to the backside of your lace, sew through the fold.
4. Gently pull the thread with one hand while holding the lace with your other hand. The lace trim will pucker and ruffle, and curve back on itself until the two short ends meet. Sew the short ends together with a few whipstitches. Knot the thread in the trim, and leave your thread end long to sew onto a project.
Here's a view of the backsides of two flowers: