West African
Cut the cassava into 5 cm chunks, split them lengthwise and remove the woody core; cut the plantains into 3-4 pieces each.
Put the cassava in a large pot, cover with water, bring to a boil and cook for 10 minutes.
Add the plantains and boil for 15-20 minutes more, until both are soft enough for a knife to slide through easily.
Drain well and pound the plantain first in a large mortar (or process it in a food processor) until smooth.
Add the cassava a few pieces at a time and keep pounding, turning the mass with wet hands and adding the cold water a spoonful at a time, until it forms one smooth, stretchy, lump-free dough.
With wet hands, shape the fufu into 6 smooth balls of about 250 g.
Serve at once in bowls of hot soup; pinch off pieces with the fingers and swallow them with the soup.