I saw this made on Ideal World, and had to have a go. I think it's a lovely effect, but it takes a long time and an awful lot of card.
Take two square cards, cut one down to form a flap. Then join together. Decorate front and inside putting the brad on before you add matting and layering inside. This will hide the workings of the brad. Cut another slightly smaller card to go inside and decorate.
The topper slips down behind the brad to keep it closed.