Flat "earthenware". Lol
Actually, Wiki says: A trencher was originally a flat round of bread used as a plate, upon which the food could be placed to eat.
Earth is flat as a trencher. Do expound!
Actually, they are traditionally made of wood.
But, you still get the cookie.
A trencher is a round wood board with no edge or lip: a French cheeseboard.
The Fathers taught earth was "round like a trencher, not round like a ball" in order to combat the error caused by the use of the words "round" and "rotundity."