Soak sabudana for 2 hrs and after that drain it and keep it aside.
On a skillet or in a shallow pan, roast the groundnuts/peanuts till they become crisp and crunchy. Cool and then coarsely powder in a mortar-pestle or in a dry grinder.
Add the sabudana in a mixing bowl.
Mash the potatoes. Mix the mashed potatoes and sabudana together.
Mix everything together and bind well.
Now take some portion of the mixture in your hands and shape them into flat round vadas or patties.
If it breaks, then add 1 to 2 tablespoons of rajgira atta (or amaranth flour) again to the mixture and mix well.
Heat oil for deep frying in a kadai.Fry it on medium flame. If this ball does not break while frying, then you are good to go.
Serve sabudana vada with sweet curd/yoghurt or green chutney. You could also serve sabudana vadas with tomato sauce.
