I've asked the question to some of the very knowledgeable cooks in La Belle, so I'm waiting to hear back. In the meantime, I did have a discussion about bread crusts while at MTA last weekend, and I was told that crusts then were made very thick and tough, because they basically served as a frame and tray for a dish, and weren't meant to be eaten by gentle folk. At the same time, they're perfectly edible and could be given away as scraps. They were also thick enough that they were used to preserve food. The inside of a thick piece of bread would remain good for weeks, even if the outside grew mold (kind of like the rind on cheese). I'm wondering if a trencher would best be made using a similar technique to these crusts.