In trying to find out how the "trencher" loaves were made, I searched for "medieval bread baking" and found this:.Soul-Making and Bread-Baking. March 15, 2000. The Connection ...
... Whether baking a classically simple French baguette or the complex struan bread
first made by medieval Celts on the Isle of Skye the metaphor holds. ...
http://www.theconnection.org/archive/2000/03/0315b.shtml

I have been unable to find a definition of the word "struan". It is a common family name.