Ancient Sardinians had a saying: Chie hat pane, mai no morit (who has bread, will never die). This is true for most of the world. Pane Carasau is one of the ancient breads they were talking about. You can imagine the ancients making this bread because of its long storage capabilities and portability.
It is a a very thin flat bread--some might call a cracker--that was traditionally made for shepherds by the housewives to carry with them for long months on high pastures with their flocks. They can be eaten with sausage and cheese, or dipped in milk to re-hydrate for colazione and drizzled with honey or jam. Pane Frattau is a soup made with shards of Pane Carasau, meat, eggs, cheese and tomato. Modern Sardinian chefs are also using pane carasau in their recipes, for instance, carasau lasagna.
The tedious method by which is is made creates a thin, crispy bread that will last literally for months, even if it happens to crack into shards along their travels. There are some who refer to this flatbread as carte della musica (music sheets) because of its thinness.
The dough itself is fairly simple: durum wheat, yeast, water and salt. It's rolled into extremely thin rounds and baked in a wood oven until the bread puffs up like a balloon, then quickly (with dexterity, not to get steam-burned) cut into two halves, making it even thinner. They are then toasted again in the oven and dried completely. Nowadays, in Italy you might even come across packaged Pane Carasau in supermarkets.