sweet red bean paste (anko)
A sweet paste of cooked azuki beans and sugar, either chunky or smoothly sieved, and the classic filling for Japanese sweets.
Anko is a paste made from small red azuki beans that are cooked until soft and then thickened with sugar. There are two main styles: tsubuan, where some beans stay whole and the skins are kept, and koshian, which is pressed through a sieve to become fine and velvety. It tastes sweet, gently nutty and slightly earthy, with a dense, spreadable texture firmer than jam. The smooth kind works better for fillings that are wrapped or shaped, while the chunky kind adds bite and more bean character. Ready-made anko comes in cans or pouches from Asian grocers and online, and dried azuki beans for making it at home are also sold in health food and organic shops.
Substitute:
There is no true substitute, because the flavour and texture depend on the azuki bean itself. The closest option is to cook it yourself from dried azuki beans and sugar, which takes a few hours but works well. Sweetened pastes from other beans or chestnut purée give something edible but clearly different.