"This is a common South Indian food that uses leftover rice. It can be had for breakfast, lunch, or as a snack. The 12 hours mentioned is just overnight soaking. The process is similar to making crepes or pancakes. You can find urad dal at most Indian grocers. Dosas are best eaten hot out of the pan and are usually served with coconut chutney and sambhar (a South Indian hearty lentil soup)."
Combine basmati rice, urad dal, parboiled rice, and fenugreek seeds in a bowl. Cover with water; soak for 2 to 3 hours.
Drain the rice mixture; transfer to a blender. Add water, 1/4 cup at a time, and blend until a smooth paste forms. Add salt. Transfer batter to a covered container; set aside to ferment, at least 12 hours.
Thin the batter, if necessary, by stirring in 1 tablespoon water at a time.
Heat 1 tablespoon oil in a large skillet over medium-high heat. Ladle 1/4 cup batter into the skillet, spreading it quickly into a circular shape. Fry until edges start to look dry and curl from the pan, 1 to 2 minutes. Flip dosa; cook until underside is just golden and still soft, about 30 seconds.