Wash the tapioca and soak it in 3 cups of water for 3 to 4 hours.
Drain the water. After soaking, the tapioca will have increased in volume, by about 2 times. Set aside.
Par-boil the potatoes, so they are only half-cooked. Insert a knife into the potato to ensure that it is still somewhat firm.
Cool the potatoes, then peel and grate them using a vegetable grater.
Mix all the ingredients together. The dough will be a little sticky and soft in consistency.
Divide the potato dough into 16 parts.
Roll each one into a smooth patty. You will need to lightly oil your palms to prevent the dough from sticking.
Heat the oil in a frying pan on medium high heat. There should be at least 1½ inches of oil in the frying pan. To check if the oil is ready, drop a small piece of dough into the oil. The dough should rise to the surface, and not change its color immediately.
Slowly drop the patties into the frying pan.
Fry the vada until both sides are golden brown. Turn them occasionally. It will take approx. 4 to 5 minutes to cook.
Remove the vada and place over a paper towel so the excess oil is absorbed.
Sabudana vada should be crunchy on the outside and soft inside.
Serve them as is or with cilantro or tamarind chutney.