1. Grind the soaked urad dal to a smooth dal until it froths up and increases in quantity.
2. Wash the idli rava and drain out all the water.
3. Add rava to the urad batter and grind further until it blends well with the batter (About 3-5 minutes). If you are using soaked white rice, drain out all the water and add to urad batter; grind until it blends well and forms a smooth paste.
4. Transfer into a large mixing bowl and let it ferment overnight or for 8-10 hours; add salt and mix well.
5. Pour into moode ele (kedige moulds) and steam cook for about 20-25 minutes.
6. Moode is done when no grains stick to the fork when pierced.
7. Remove from stove and serve hot with coconut chutney, sambhar, gashi or any other side dish of your choice.

Note:
If you are grinding urad dal using the blender, it generally takes about 10-15 minutes for the batter to froth up. Make sure you stop every 5-7 mins and mix with a spatula. In case of a grinder, it takes about 25-30 minutes. While storing the batter for fermenting, make sure the bowl is large enough to accommodate the rise in batter quantity.
While pouring the batter into moode ele, fill it only up to three fourths.... Moode will rise further while it cooks.
I use a pressure cooker (without weight) to steam idlis and moode.
You could also use idli cookers that are available in the market.
In either case, add enough water at the bottom to withstand 20 minutes of steaming.
It is important to ensure that moode ele stays upright while it cooks.
You wouldn't want the moode to fall off and let the water from the bottom of the cooker get in. So, I place each moode separately inside long steel tumblers.
To remove the moode from the mould, slowly pull out the tiny sticks that hold the mould together; the mould will fall apart automatically.

Courtesy: http://maneadige.blogspot.com/