Red bean paste — anko in Japanese, dou sha in Chinese, pat in Korean — is a sweet, dense paste made by boiling azuki (adzuki) beans until soft and cooking them down with sugar into a thick, spreadable confection the deep red-brown of the beans themselves. It is the foundational filling of East Asian sweets: packed into mochi and daifuku, folded into dorayaki pancakes and steamed buns, spooned over shaved ice, and piped into countless pastries. Mildly sweet, earthy and faintly nutty, it is less a candy than a building block from which a whole tradition of confectionery is assembled.