It's the sweet descendant of a much older savory pastry called sanbosag — the same ancestor that, carried along old trade routes, eventually gave the world the samosa.
A dough enriched with yogurt and butter is filled with ground almonds or walnuts, sugar, and cardamom, folded into a crescent, and deep-fried until golden, then dusted with powdered sugar. Yazd's bakeries sell it year-round, with sales spiking around the Persian new year.