Pane guttiau is the crisp answer to its layered Sardinian sibling: the same pane carasau, kept hard instead of softened. Carasau is the brittle parchment-thin flatbread of Sardinia, baked twice so it snaps cleanly. To make guttiau, a sheet is brushed with olive oil, scattered with coarse salt, sometimes a little rosemary, and passed back through heat just long enough that the oil and salt set into the surface and the sheet crisps further. The defining choice is the opposite of pane frattau: nothing here is allowed to go soft. The texture of the finished thing is entirely the shatter of the bread.
The craft is the oil, the salt, and the second pass of heat. The oil is brushed thin and even so it gilds the sheet rather than pooling and turning a patch greasy; too heavy a hand and the carasau goes from crisp to limp. The salt is coarse so it stays as distinct points across the surface instead of dissolving into a uniform saltiness, and rosemary, when it is used, is kept sparse so it scents rather than dominates. The reheat is brief and watched, because carasau is already a baked-dry bread and a few seconds too long takes it from toasted to scorched. It is eaten soon after, while the oil-crisped surface is at its sharpest, broken by hand into shards rather than cut.
The variations stay in Sardinia and stay spare: the plain oil-and-salt sheet against the one scented with rosemary, the version dusted with a hard cheese over the hot oil, the sheet served alongside a soft cheese or cured meat so the brittle bread does the structural counter-work. Its soaked sibling, the same carasau layered with tomato, pecorino, and egg, is pane frattau. Each of those is a different decision about the same Sardinian sheet, and each deserves its own article rather than being crowded in here.