Cut the manioc root into large (10 cm long) chunks, then peel, making sure to remove the inner skin (just under the thick brown outer skin).
Using a large knife, split the chunks lengthwise into halves, or quarters for very big pieces.
Cut the plantains into three equal pieces, and peel (this can be a pain, but use a knife to get the peel off.
Alternately, you can steam the plantain then remove the peel).
Add the manioc and plantain to a large pot in a steamer basket, or directly on the bottom of the pot.
Add 2 cm of water in the pot, and bring to a medium simmer.
Cover and steam for 40 minutes, remove and pile on a platter.

Goes well with anything that you would normally serve potatoes or rice with, and is very inexpensive to make.