Cut the potatoes and taro into small cubes and then steam with high fire for 20 to 30 minutes until soft.
Smash taro well, mix in sugar when the taro is still hot. Add sweet potato starch in. Knead to form a soft ball, add water if needed. Add more flour is your mixture is too wet and more water if the mixture is too dry.
Then divide the dough into 4 equal portions, shape each one into thin long log (around 1.5cm in diameter). Then cut into small dices. Dust some corn flour or sweet potato starch to avoid them from sticky together.
To cook the trao balls
Bring a pot of water to a boiling, and then gently lower the balls in. Add 2 tablespoons of cold water when the taro balls floats. Then continue cooking for 2-3 minutes.
In the meantime, add 2 slices of ginger and 1 pieces of brown sugar. Bring to a boiling.
Scoop the syrup water in serving bowl and transfer the taro balls out once cooked.