Soak both rice together and dal separately in bowl to cover them about 2" deep. Soak 8 hours or overnight.
The next morning, drain all the water from the rice and urad dal. Wash two three times and drain and put some in a food processor/ grinder and grind - adding very little water if necessary - to a smooth yet slightly grainy paste. You need to grind both rice and dal separately.
When all the rice-daal mix is ground like this, put it into a large mixing bowl and add enough water to make a batter. The consistency of the batter should be such that it thickly coats a spoon dipped in it.
Keep dosa batter aside in a warm, dark spot, covered, for 6-8 hours. After this fermentation, stir the batter well and add salt. It is now ready to make Dosas.
Heat skillet, then add a little oil in the skillet and brush well with kitchen towel through all the sides to grease the pan.
The correct amount of oil is such that it is barely visible on the pan. Now turn on the heat/ flame at medium high.
Fill ¼ cup of batter in the ladle. Gently pour this batter onto the center of the pan - just as you would for a pancake - till the ladle is empty.
Now begin to spread the batter in sweeping circular motions to form a pancake of roughly 8" diameter. Do not be alarmed if the Dosa develops tiny holes as you spread the batter. This is normal.
As soon as you have finished spreading the batter out on the pan, dip the basting brush in cooking oil and drizzle the oil all over the surface of the dosa and also around its edges.
When the upper surface begins to look cooked (it will no longer look soft or runny), flip the Dosa. By this time, ideally, the surface that was underneath should be light golden in color.
Allow to cook for 1 minute after flipping.
Continue make the dosa by greasing the pan again and then add batter then oil and filliping the other side and cook until you finish the entire batter or make enough dosa you need. You can refrigerate the batter for future use.
Serve the ready Dosa with side dishes like Coconut chutney, Idly milagai podi and sambar.