Sangak

Sangak or nân-e sangak (Persian: نان سنگک) is a triangular Iranian whole wheat leavened flatbread. In Persian sangak means "pebble". The bread is baked on a bed of small river stones in an oven. There are usually two varieties of this bread offered at Iranian bakeries: one that has no toppings; and a more expensive variety traditionally topped with onion seeds but more commonly with sesame seeds, or, more rarely, with cumin, black cumin, caraway or even dried aromatic herbs. Sangak bread was traditionally the bread of the Persian army. It is mentioned for the first time in the 11th century. Each soldier carried a small quantity of pebbles which at camp were brought together to create the "sangak oven" that would bake the bread for the entire army. It was eaten with lamb kabab.

Source: Wikipedia