There isn't a foodstuff more synonymous with San Francisco than sourdough, and yet there aren't so many places using the naturally fermented dough for anything beyond the round loaves that make up the city's bread bowls. Now Arizmendi Bakery — already an only-in-S.F. phenomenon thanks to its horizontal, worker-owned management — has started baking buttery, flaky croissants using the city's signature dough. Its tangy flavor is most apparent in the plain sourdough croissants, though it also adds complexity to its chocolate and almond variations. If there's a better reward for a Saturday bike ride through the park, we have yet to find it.