Soak them overnight or minimum 8 hrs. Soak them separately.
Take tur dal, chana dal, and methi seeds in another bowl and soak them.
Wash and clean urad dal and soak it overnight in a separate bowl.
Grind rice and mixture of dal separately with minimal required water; otherwise, the mixture will not be as smooth as needed in the dosa batter. After grinding them separately, transfer them into a large mixing bowl.
Mix water to make the batter a thick but flowing consistency. Consistency should neither be very thick nor thin, as it will be difficult to spread on the dosa pan.
Add salt as per taste and mix thoroughly.
Now cover it with a lid and leave overnight outside for fermentation. After fermentation the batter will be lighter and fluffier.
Put a flat pan on heat. Keep it on low flame. Add 1 teaspoon of oil and one ladle of batter to it and then spread the batter evenly. If the pan is very hot, it will be difficult to spread the batter evenly. Hence, Keep a bowl of water along with it, sprinkle a few drops on the pan, and wipe it off with a clean cloth to avoid excessive heating of the dosa pan.
Sprinkle a few drops of butter or oil over them.
Once the dosa is cooked, the sides will automatically leave the pan. Then take it out on a plate.
Repeat for all the batter. Plain dosa is ready.
Potato Masala for Stuffing in Dosa
Heat oil in a frying pan.
Add mustard seeds and cumin seeds and let it splutter.
Add hing (asafoetida) to it.
Then add green chilli, ginger and garlic chopped, curry leaves.
Add sliced onions and fry for 2-3 mins till it turns brown.
Add mashed potato, mix thoroughly, and sauté for another 2-3 minutes.
Then add turmeric powder and salt to taste.
Once done, remove from flame and keep aside to cool. Masala is ready to serve with Dosa.
Preparation of Sambar
These are the basic ingredients for sambar.
Pressure cook toor dal until cooked (3-4 whistles), adding turmeric powder and salt. You may add vegetables like brinjal, pumpkin, Drumsticks, and tomato along with dal.
In the meantime, make tamarind paste by soaking it in hot water. Squeeze the pulp into water and remove seeds if they have.
Heat oil in a pan. Add one tsp mustard seeds and cumin seeds and let it splutter. Add one tsp hing or asafoetida.
Add curry leaves, crushed garlic and ginger. Then add sliced onions and green chillies. Saute for 2 mins.
Add chopped tomatoes and saute till it's cooked and mashy.
Next, add ½ tsp red chili powder and 2 - 3 tbsp sambar masala.
Then add tamarind paste and diced tomato into the pan and let it simmer for 2 – 4 min.
Add cooked dal and a little water if it has a thicker consistency.
Bring it to a boil for 3-4 mins. Add salt as per taste. Garnish with chopped coriander leaves.
Serve hot masala dosa with sambar coconut chutney.