Rinse sabudana under tap water until the water runs completely clear. Transfer the sabudana to a large bowl. Add water to sabudana. Just enough to cover them.
Cover and leave it unattended for 3-5 hours.
After the soak cycle is done, combine sabudana with boiled potatoes.
Stir in Singhara flour, green chilies, cilantro, and spices.
Mix well until evenly blended.
Heat oil in a kadai. Cut a plastic bag.
Pour few drops of oil over it.
Take a small ball of sabudana mixture. Flatten the ball and make it look like a tikki.
Using your finger make an indent in the tikki. It will now look like a vada/bhalla.
Carefully lift the vada and fry in hot oil until golden brown. Make sure the oil is not too hot. The trick is to cook in medium-hot oil until golden brown, occasionally turning with a slotted spoon.
When done, remove the crispy vadas from hot oil with a slotted spoon and set aside to drain on kitchen paper. Repeat the process with rest of the dough until all the mixture is used up.