In a bowl, soak rice and dal for 4-5 hrs after washing it 3 times.
Grind it rice with soaked poha and water. Grinded mixture should be coarse
Grind dal with little water and make a smooth and fluffy batter.
Mix both batters in a bowl with your hand. Keep the batter for 7-8 hrs or overnight for fermentation.
When the batter is fermented will stir well and add salt, sugar and required water to adjust consistency.
Heat oil in a pan, add mustard seeds, cumin seeds, soaked chana dal and soaked urad dal. Sauté till the dal is slightly golden brown.
Then add asafetida, ginger paste, chopped green chilli, curry leaves and sliced onion. Add boiled potatoes, turmeric powder, salt and little water. Mix well. The potato masala is ready.
Heat tawa, add 1 tsp oil and with decrease tawa temperature with a wet cloth. Now pour 2 ladles full of batter and spread evenly. Then apply batter and place potato masala in the centre. Cook until the dosa becomes golden brown. No need to flip.
Serve masala dosa with chutney and sambhar.