Keluak is the fermented, detoxified seed of the tall Southeast Asian rainforest tree Pangium edule — a large nut that is violently poisonous when fresh and must be boiled, buried and aged for weeks before it turns edible. Cracked open, the cured kernel is inky black, soft and oily, with a deep, brooding flavour of truffle, dark chocolate, mushroom and earth; it is the black heart of Indonesian rawon beef soup and Peranakan ayam buah keluak, dishes that are unthinkable without it.