I'm quite excited because I've finally managed to figure this out.
It's been boggling me for months since my teacher Adeline taught me the round and backed case binding technique (which I have failed badly in making after leaving her studio).
I had initially experimented the *quarter case binding with cloth, which did not work out. But I am really happy to see the results from this session, although maybe not technically sound, but with paper.
From here on, my task is to find out how to work this technique with fabric.
*A style of bookbinding in which the spine is bound in a different material than the sides, usually a more durable covering such as leather, often in a contrasting color, extending no more than one-eighth of the width of the boards.