Try to use a little fry pan to get to a closer size of the burger, or you can cut off the excess once ready.
Cook the Brazilian Tapioca on tradition way as following:
Heat a fry pan over medium heat for at least a minute.
Take aprox. 80g of Brazilian Tapioca and sift over the fry pan equally.
Leave it for about two minutes or until the edges start to curl up. Then take off the pan and do it again, so you will have to Tapioca bun.
Bake for around 25 minutes or until golden.