Shirako is the milt — the sperm-filled reproductive sacs — of male fish, above all cod and pufferfish, and it is one of Japan's most prized winter delicacies. Cool, pale ivory-to-cream lobes gathered in soft, brain-like folds, it eats like a savoury seafood custard: silken and barely set when raw, turning warm, molten and lightly custardy when poached or grilled, with a clean marine sweetness, a deep briny umami and a lush, cream-and-butter richness that has earned it comparisons to foie gras of the sea. The word literally means "white children," and the same ingredient travels under gentler nicknames — kumoko ("cloud child") for cod milt in Hokkaido and the poetic tachi in the north — a soft-spoken vocabulary for a food many first meet with hesitation.