Wash sabudana under running cold water till water runs clear. Then soak sabudana in hot water for 1 1/2 hours. (Sabudana should be very soft. When you press them it should be mash easily as shown in picture below.)After that drain it and keep it aside for later use.
Dry roast the peanuts till it is light brown. Let it cool a little bit. Then add peanuts to food processor and process it till coarse crumbs.
Take that crushed peanuts in a bowl. Add chopped cilantro, green chilies, ginger paste, garlic paste and salt. Then add boiled potatoes.
Mix well and make dough. Divide the dough in to 12 equal portions. Take some oil on you palm and grease it. Then roll between your palm and make even size and shaped patties.
Meanwhile heat the oil in a pan for deep frying on medium-high heat. The oil should be little hotter than usual frying. Once hot add vada in to hot oil gently. Add 3-4 at a time. Let them fry on both sides till they are crisp and golden brown. Then remove them on paper lined dish. It will take about 5 minutes approximately to fry.
Make sure that sabudana are soaked well. Check it by pressing the sabudana and it will mash easily.
Make sure that you drain the sabudana well after soaking it. Otherwise the dough will be sticky.
Do not over fry them otherwise they start to break from the center.
Make sure that oil should be hot enough.
Serve with ay chutney or Ketchup.