Peel the purple sweet potato, slice it, steam it in a steamer, take it out while it is hot and press it into a puree, add an appropriate amount of tapioca flour, (you can add an appropriate amount of sugar if you like dessert), and knead it into a smooth dough. If it is too dry, add a little water and poke into it. Strips, cut into small pieces, and serve as taro balls. After boiling water in a pot, put the taro balls in a pot and cook for about 3 minutes. They will float and they will be cooked. Take out and soak in cold water for a while. To taste better, you can use cold boiled water several times, and you can add it yourself, such as milk red bean soup, etc.