Sweet Potato Balls

I saw this recipe in my cookbook "Taiwan Night Market Snacks", and I thought to give it a try. I couldn't find sweet potato starch in the supermarket, instead I used tapioca starch. I don't know if I did it right, the outcome is sort of chewy (knowing tapioca is one of the ingredients in making bubble tea).

Here's the recipe:
sweet potato 500 g (2 pieces)
sweet potato starch 400 g ( I used tapioca)
brown sugar (I used 1 cup)

Cut sweet potato into cubes. Steam until soft and pound it in puree.

Add sugar and sweet potato starch, whisk well to blend. Knead into long cylinder; cut for about 1.5 cm cubes.

Deep fried sweet potato cubes in oil for about 30 seconds; stir rapidly and press cubes lightly to make cubes into balls. Transfer to plate and ready to serve.