A tongue is made on the book-block and a board is glued and placed on the tongue/paste-down up to the hinge line. The book is rounded but not necessarily backed.

Philip prefers rounded, unbacked, spine methods, as backing the sections over to a sharp 'hook' can injure the paper. Rounding simply compensates for natural swelling due to sewing, and guards, if used. The board may take a slight cushion bevel or tapering on the inside to accommodate the swelling. This slot-less attachment is often now called a 'simplified' binding method, the board being glued directly on to the end section upper leaf, called the 'waste' or protective end-leaf (as it is often torn away).

click for larger image
Non-Duality As It Is
by Philip Smith, 2006
Bound 2007
Example of semi-tongue-in-slot board attachment