Bappir
Bappir was a Sumerian twice-baked barley bread that was primarily used in ancient Mesopotamian beer brewing. Historical research done at Anchor Brewing Co. in 1989 (documented in Charlie Papazian's Home Brewer's Companion ()) reconstructed a bread made from malted barley and barley flour with honey, spices and water and baked until hard enough to store for long periods of time; the finished product was probably crumbled and mixed with water, malt and either dates or honey and allowed to ferment for a few days, producing a somewhat sweet brew. It seems to have been drunk flat without bottling or conditioning with a straw in the manner that yerba mate is drunk now. It is thought that bappir was seldom baked with the intent of being eaten; its storage qualities made it a good candidate for an emergency ration in times of scarcity, but its primary use seems to have been beer-making. A modern interpretation of Sumerian bappir bread was brewed and bottled in 2016 by Anchorbrew. See also

Ninkasi, the Sumerian goddess of beer
Biscotti, a similarly twice-baked modern bread that is often eaten as a sweet course with wine or coffee

References

Breads
Brewing ingredients
Twice-baked goods