Wash and clean raw rice and boiled rice. Soak together in 2 cups water for 4 - 5 hours.
Drain out water and make a smooth paste with grated coconut and salt. Sprinkle very little water when making batter (1 - 2 tbsp).
Transfer the dosa batter into another vessel. Polo batter should be of pouring consistency (slightly thinner than normal dosa batter).
In a dosa tawa, heat little oil. Pour a ladleful of the batter into it. Spread evenly with circular rotations using the base of the ladle, starting from the centre and progressing outwards. Close with a lid.
Allow to cook for about 30 seconds, before sliding the dosa off the pan. Repeat the process with the remaining batter.
Cut polo/dosa into thin strips or 1-inch squares or rectangles. In a wide bowl, mix dosa pieces with melted and sieved jaggery with finger tips. Sprinkle cardamom powder, rest for 30 mins and serve.