Glue six large matchboxes side by side on edge onto the corrugated cardboard. Do not glue the boxes together, otherwise they cannot be opened later. Glue six more boxes on top of them to make a rectangle. You can now cut off the rest of the corrugated cardboard.
Place the template on the matchboxes and trace it with a white Posca marker. If you wish, you can now decorate the surface with stamps.
Glue the small matchboxes to the top edge. This way, all the matchboxes can be pushed open. Decorate these boxes with stamps too.
Write numbers on each matchbox with the Posca marker.
Finally, stick on a few star stickers as desired.