Step 1: Cut & attach fiberboard and foam
Dave sawed off the tips of wood that jut out at the top of the frame so we'd have a neat, rectangular shape to start with. Then he took a piece of plain ol' fiberboard and cut it the same size as the headboard so I'd have something to upholster over. A mist of spray-mount holds the foam in place.
Step 2: Add the layers of foam and batting
A layer of batting, also spray-mounted to the foam layer underneath to keep things from shifting around.