Wash and soak the rice for at least four hours. Wash and soak the dal for 2 hours. Wash and soak the poha for one hour. Drain rice, dal and poha. Grind each one separately to a fine consistency.
Mix all the three well and add water as required to make a batter of desired consistency. Transfer the batter into a deep vessel, cover with a tight fitting lid and keep it in a dark and warm place overnight to ferment.
Just before making the dosas, add baking soda, sugar and salt and mix lightly. Heat a non stick tawa. Drizzle a little oil and wipe with a wet cloth so that the tawa is tempered.
Drop a ladle full of batter on the tawa and spread it in a circular motion as thinly as possible. Drizzle a little oil all around and let the dosa cook on medium heat.
When ready the edges will begin to separate from the tawa. Gently roll up and serve hot with chutney and sambhar.