Wash and soak rice in plenty of water for about 4 to 5 hours.
Wash and soak urad dal for 2 to 3 hours along with fenugreek seeds.
Drain urad dal and reserve the water to use it for grinding. In a grinder/blender grind urad dal and fenugreek seeds to form a smooth and fluffy batter. (During grinding, add 1/4-cup water at a time as required. I used about 3/4-cup water.) Transfer this urad batter to a large bowl.
In the grinder ,grind together drained rice, cooked rice and just enough water to form a smooth batter. (Add 1/4-cup water at a time, as required. I used about 3/4 to 1 cup water.) Mix the rice batter along with the urad dal batter.
Add salt to taste and mix well.
Keep the batter aside to ferment in a warm place for about 10 to 12 hours. The bowl should be large enough to accommodate twice the volume of the batter. After fermentation the batter will be light and fluffy.
This is the basic recipe for dosa batter. Use sufficient quantity of this batter to prepare masala dosa. You can refrigerate the remaining batter for later use.
To prepare masala dosa:
Heat a pan lightly brush it with oil. (If you are using a non stick pan, do not apply oil on the pan, if you do so you will not be able to spread the batter)
Spread a ladle full of batter to form thin and large circle. Drizzle oil or ghee over the dosa (use ghee for best results)
When it is cooked and the edges start to brown. Place 2 to 3 tbsp. of the potato masala over the dosa,
Fold the dosa and serve with sambar and coconut chutney.