Soak sago overnight, the water level should be just for the sago to immerse fully, do not add more water. Soak at least for 4-6 hours.
Next day morning you can fluff it up, if you press a pearl it should be easily mashable. Rinse it well ,drain water and set aside.
Now roast peanuts until golden brown, remove the skin and transfer it to the mixer jar.
Pulse it until you get a coarse mixture. Set aside.
Rinse potatoes, cut each into half and pressure cook for 4-5 whistles or until soft. Peel off the skin and mash it up well.
In a mixing bowl add sago, mashed potato, jeera powder, lemon juice, ginger, coriander leaves and salt to taste. Mix well. If it is too dry sprinkle little water.
Make big lemon sized balls.
On a piece of parchment paper, place a ball on it pat it with your fingers to form a slightly thick roti. If it sticks drizzle few drops of oil on the sheet. Gently remove it.
Heat the dosa tawa, and carefully transfer the roti to the tawa.
Drizzle oil, cook until both sides are golden. Cook in low medium flame as it will take time to cook at least 3-5mins per roti. Repeat to finish. Serve Sabudana Thalipeeth hot.