Cut sweet potato into chunks, place in separate bowls and steam until they soften, about 20 minutes.
While they're still hot, transfer the both kinds of sweet potato into separate mixing bowls, then add in sugar and butter in each bowl. Use a potato masher or fork to mash until you reach the consistency of mashed potato.
Add tapioca flour in each bowl, mix and knead to form a ball. If the dough is too wet, add more tapioca flour; if it's too dry then add some water.
Preheat oven to 350°F (180°C)
Form the dough into 1 inch little balls and place them on a baking pan lined with parchment paper or silicone mat. Moistening your hands a little bit will make rolling the ball easier.
Bake for 16-18 minutes or until the bottom part is golden brown. Let cool for 5 minutes before enjoy it.
