Step 3: Muffin top
Trim it so it will fit loosely inside of the walls of the base. It will fit snug once the fabric material covers everything.
Get some additional foam pieces or a big ball of batting to form the curved plushie top for the button.
Cut two pieces of fabric that will cover the top and bottom of the button.
Sew around it following the edge of the cardboard form.
You can trim the excess on the corners as the edge will be folded under and tucked into the base.
I ran the edge through a serger to finish it. The serger binds the edge and trims it at the same time.