Soak the rice and black gram for 2 hours. Wash the black gram. No need to remove the skin of the black gram.
If using Indian Wet Grinder, add the rice and grind for few minutes. When the rice reaches a coarse consistency, start adding the soaked black gram in an even stream. The grinding process will be quite noisy for a while. Grind to a smooth batter using enough water. Allow to ferment overnight.