WARNING: This dish is not suitable for beginners and can be quite technical
Urad dal (Black gram split & husked)-1 cup
Rice flour-2 cups
Baking Powder- 1 teaspoon
Cooking Oil/Butter-1 tablespoon per dosa
Soak the Urad Dal in two cups of water over night or for at least six hours. Take out the soaked dal from the water, put it in a blender, and blend well using some water BUT DO NOT LET IT BECOME TOO WATERY. The batter should feel absolutely smooth to the touch.
In this mixture, add the rice flour and some water and switch on the blender again to turn this all into a thick batter which has a pouring consistency. Pour the mixture into a suitable vessel, cover it and let it ferment (that is let the batter puff up) for the next 12 to 24 hours, depending on what the ambient temperatures are. If it is too cold, then wait for 24 hours and go ahead. Add the salt and baking powder, when you are ready to cook.
In a large non-stick girdle, spread about half a cup of batter evenly. Light the fire now. Let the dosa cook. Add the oil on the top side and a little on the corners. Do not disturb the dosa till it starts browning. You can then gently nudge the dosa at the edge and it will come out on its own when it is done. Remove the dosa to a plate. It is greater fun if you can eat it right away, with some masala filling and coconut chutney. Add sambar too for a full authentic South Indian experience.
For the next dosa, you will need to cool down the girdle OTHERWISE YOU WILL NOT BE ABLE TO SPREAD THE BATTER. To do so, therefore, wash the girdle in cold water and follow the above mentioned method again.