This lightly sweet sandwich bread with a crunchy topping is certainly unique, but does it have to be unique to San Francisco? The hallmarks of this San Francisco roll are its soft, chewy crumb and the mottled, crackly appearance that gives rise to its crunch. Developing a recipe for the soft, chewy crumb was the easy part. The topping—an odd mix of water, oil, sugar, salt, rice flour, and yeast—was the challenge. The ingredients need to be combined in the correct proportions to keep the…