In a bowl, mix together the dry ingredients - wheat flour and rice flour, baking soda and salt until well mixed.
In a blender, grind together the cooked rice, yogurt and water until you get a smooth mixture.
Transfer the wet mixture to the dry flour mixture and slowly mix in the ingredients without forming any lumps. It is important that the dosa batter should have a smooth consistency without lumps. You can use a balloon whisk to mix the batter, which will help you achieve a smooth texture easily.
Now this instant dosa batter doesn't need any fermentation and you can use it right away to make the dosas if you wish, however you may also cover the bowl and keep it closed for about half an hour for better results (this is not necessary though).
Once the batter is ready and you are ready to prepare the dosa, heat an iron pan or non stick pan, grease with oil or ghee.
Add one to two ladles of instant dosa batter to the pan, and spread in gently in circular motion, just like you make for regular dosa. However, do not try to fill in any gaps with the batter, as that is totally fine.
AS the dosa begins to set in about a minute, add one or two teaspoons of ghee or oil, which will help to make the dosa more crispy.
Once the dosa is cooked on one side, gently flip the dosa, starting from the sides and moving inward, and cook the other side too which will cook more easily.
Serve the dosa hot with sambar, chutney or any of your favorite side dishes, enjoy!