Place the unpeeled cassava tubers in a large pot. Cover with cold water and bring to a boil. Let boil for 15 to 30 minutes until cassava is cooked through.
Drain cassava. Allow to cool somewhat and peel. Place cassava into a large bowl with the butter, salt, and pepper. Mash with a potato masher until very smooth.
Place mixture in a serving bowl. To eat, wet hands with water, form into a ball, and dip into a stew or sauce.