Peel and grate cassava using the large or medium setting of a grater.
Place grated cassava into a cheesecloth or clean kitchen cloth and squeeze out as much liquid as possible.
In a large bowl, combine the grated cassava, dulong, leeks, wansuy, and egg. Season well with salt and pepper. Mix until everything is well combined.
In a large pan/wok over medium heat, heat the oil and scoop the okoy mixture carefully into the oil.
Fry the okoy for a few minutes each side, until golden. Drain excess oil on paper towels.