The breadboard ends are 1020x150x40mm made from the same timber as the edging. Being oversized in length allows me to trim them back precisely when the top is finished and gives me a lip to grip to remove the board while fitting.
The technique I used was fairly standard. I used a drill press and a forsner bit to remove the bulk of the deep mortises. I squared the edges with a set of bevel chisels. Finally, I used a 6mm router bit to slowly make the long 10mm groove. Unfortunately I didn't get any photos of the progress shots.