Mucuna glabra

Brazil (northeast): flour is made from both the seeds and roots. The seeds are placed in a clay pot and roasted in hot ashes or hot sand, until they pop. They are then hulled and pulverized in a mortar. The flour is then sifted and washed in successive changes of water to remove the toxic element. The wet flour is then squeezed to remove excess moisture and, finally, dried over a fire. Flour is made from the root in a similar manner. The roots are quite large, often reaching the size of 30 centimeters in length. Occasionally, a single root may produce more than a ton of flour. The flour or starch thus obtained is made into a variety of Brazilian foods including farofa, in which the meal is sautéed and mixed with bits of meat, crisp fat, chopped egg, &tc.; boijus, which are small, sweet cakes; and angus, which are dumplings, the flour being merely boiled in water.

Note: the name of this plant is in doubt. For details, see http://www.theplantlist.org/tpl1.1/record/kew-2375481