Made with white beans instead of adzuki, the shiro an version of an pan is the pale, gentle one. The baseline bun asks for red bean paste; this reading swaps in shiro an, a paste cooked from white kidney or navy beans that comes out ivory rather than dark, milder in flavor and rounder in sweetness. The enriched roll is the same soft, faintly sweet bun, but the filling no longer has the deep, slightly mineral edge that adzuki brings. It is softer-spoken, sweeter on first taste, and easier to flavor with other things because it does not fight them. The bread and paste still depend on each other in the usual way, but here the balance tips toward delicacy.
The craft is in keeping it clean and pale. White bean paste discolors and turns muddy if scorched, so it wants gentle, patient cooking, the beans simmered soft, mashed or strained, then sweetened and reduced to a smooth, pliable paste that stays light in color and even in texture. Because shiro an is sweeter and less assertive than red bean, a good baker watches the sugar so it does not collapse into flat candy with no bean character left. The bun wants the familiar tender crumb, thin burnished top, and a tight seam so the soft paste does not weep into the base. A good one is mellow and balanced. A weak one is just sweet, with the beans cooked into anonymity and nothing underneath the sugar.
Because it carries other flavors so willingly, shiro an is also the base many seasonal versions are built on, tinted and scented rather than left plain. Its closest contrast inside the an pan family is the darker, earthier red bean styles, smooth koshian and chunky tsubuan. The flavored editions, the grassy matcha and the salted, floral sakura, are often shiro an underneath, and each of those deserves its own article rather than being crowded in here.