I grew up on a family farm with a grand father that was very traditional German, so I got a very old fashioned education in farming early on. Many of our staple foods were developed for storage and transport cabilities. From honeyed oats that became granola to cookies which were high calorie, spoil resistaint, at yup sometimes yummiest, but think molasses and honey rather than sugar, to preserves and dry cured meats. So I agree with Sir Ian, a trencher is a hollowed out loaf, but there may have been hearty or well seasoned versions to increase storage value or cover the taste of rancid, salty, or just meals a bit past prime.
The mention of thinking of brad as a cheese and just cutting the mold off is very accurate, just as true as often eating larva infested breads as well, more common than I want to think about. Indeed any flour stored a month or so would have larva in it simply due to the open milling and open storage conditions, modern feeds store a bit better but that has a lot to do with how we process all grains today.
We had very hearty breads that were traditionally made into bowls, these were heavy whole grain and molasses loafs that my grandfather liked heavy stews in. These were not generally today's version of stew, but often made with sweet meats, as he wasted little of and animal we butchered. I actually miss some of these items that you just can't find, very difficult even in Amish regions, not because they don't eat them, but more that the English do not, pickeled heart anyone.
I do not doubt that someone didn't make flat breads into plates at some time, seems a natural thing actually if you make such breads. Sourdough is certainly period as keeping and making starter that would develop wild yeast and thereby offer a rising was absolutely the way it was done.
I ponder this, how did cultures isolated from seas, being far inland, without mining, did they acquire salt other than trading....
