A pressing board is a tool used mostly in sewing to iron oddly shaped and inaccessible corners.
For some more info on pressing boards see
Step 1: Cut out the pieces
I cut them out of an oak board I had in the garage. You could scavenge some old furniture, but keep in mind that you would need to get off all the old finish since you'd use a hot iron and some possibly white fabric on it...
The holes at the head end of the screw are drilled a touch oversize so the screws can pull the boards nice and snug rather than binding in both boards.
I uploaded a .pdf with the pattern I made and used and you can tweak it of just make your own. It doesn't require a lot of precision, but I wanted it so that with my 3/4" thick board the whole thing still ended up being as the same size on all 4 small sides, and so that the three prongs at one end would line up so it can stand on end. Maybe you want something slightly different?
I used boards that were just under 6" wide so I scaled my drawing to make good use of the material. You could probably go an inch smaller or as much larger as you want and it would still work.