The first thing you will need to do is to cut out a circle. Here I used my Coluzzle circle template and Coluzzle knife, but you can use any tool you have that will allow you to cut a circle such as: circle scissors plus, large circle punch, Cricut, etc.
The next thing you will need is a pair of paper snips (or other sharp scissors), and a corner rounder punch. This is my favorite corner rounder punch for this technique. SU does have a larger one and it will work, but your scallops will be larger.