Well, the inside square is actually lose (3-D) and needs to be sewn down. You can either sew it down straight (topstitching, as she says) or you turn the edge in for the curved cathedral window look.. I actually did a more involved version of this using the faux-cathedral window youtube instruction.
http://www.youtube.com/watch?v=DvXUvKIzYZY
It takes longer than 10 minutes, but I love the look.