I have been doing these for years and find that the easiest way is to applique your plate to the background first.
then add your center(if you add the center then try to applique your plate you get pleats and puckers!
to get the center use fusible,light interfacing or just a muslin cut the same size as your center right sides together sew slit the fusible or muslin and turn,
then apply to the plate and background.
I cut some of the background fabric away to keep the bulk down when quilting.