bonito flakes
Dried, smoked and fermented skipjack tuna shaved into paper-thin flakes, with a smoky, deep, fishy savouriness.
Katsuobushi is skipjack tuna that has been simmered, smoked over wood, dried and often fermented with a mould culture until it is as hard as wood; it is then shaved into thin flakes. The flakes taste smoky, salty, fishy and intensely savoury, and they are the backbone of dashi, the Japanese stock made together with kombu. Scattered over hot dishes such as okonomiyaki or tofu, they curl in the rising heat and appear to dance. They are sold packaged in Asian grocers, well-stocked supermarkets and online, in large bags for stock or in small portion packs for sprinkling. Once opened, keep them airtight and dry, as they absorb moisture and lose their aroma quickly.
Substitute:
There is no equivalent substitute, because the smoky fish flavour is unique. For dashi, a plain kombu stock with dried shiitake gives savouriness and is vegetarian, but it tastes milder and earthier and lacks the smoke. Instant dashi granules usually contain bonito themselves and come close, though they are saltier and flatter. As a topping, crumbled nori can stand in, tasting of the sea rather than smoke and without the dancing effect.