Once your plate is made find something large enough to cover the raw edges.
Trace onto a piece of thin cardboard or template plastic. I like the type of template plastic you can use an iron with. Cut out your template circle and trace onto the wrong side of your circle fabric. I like using a piece of fine grit sandpaper underneath so the fabric doesn't tug when I trace.
Thread a long piece of thread through your needle and tie one end. Now baste stitch near the outer edge of your circle.
Once you've done that lay your circle template in the center where you traced your circle and pull you thread taut. Press the back and the front.
Gently remove your template and press again if neccessary. Also you may need to give a gentle pull on your thread to get your "perfect" circle shape after having removed the template.
Your circle is only as perfect as your cutting. I will never make a perfect circle but I've learned to live with it. If anyone cares then that's their problem. :o)
After your dresden plate is appliqued down onto your background fabric, pin your circle and applique.
Now to address a recent comment about the number of blades to use. Blogless Me is "no reply and no name" so I can't reply directly to her. Apparently she clicked to enlarge my dresden plate photos when I first shared them and counted the blades in each plate. So yes, she did discover some have 21 blades and some have 20. I was having trouble at first so 2 of my plates have 21. After cussing and fussing and fiddling I adjusted the needle placement on my machine and was able to get 20 blades to lay flat. It really doesn't matter how many blades in my opinion as long as you get it to lay flat. I never figured anyone would really count.
I'm back to work on my plates.