boil or steam 2 large potatoes in a pressure cooker or steamer. if pressure cooking, then pressure cook for 5 to 6 whistles.
when the potatoes are still warm, peel and crumble them. you can also chop them and keep aside.
peel, rinse and thinly slice the onions. also chop the tomatoes, ginger, green chilies and coriander leaves. rinse and dry the curry leaves in a kitchen towel. chop the cashews.
heat 2 tbsp oil in a pan or kadai/wok. lower the flame and add 1 tsp mustard seeds. crackle them.
then add the 2 tsp chana dal, 1 tsp cumin seeds and 1 tsp urad dal (optional).
stir and saute till the dals become golden.
add 2 tsp finely chopped ginger, 2 to 3 tsp chopped green chilies and 10 to 12 curry leaves.
then add 8 to 10 cashews, which have been chopped
stir and then add 1 cup tightly packed thinly sliced onions.
add a pinch of asafoetida and 1/3 to 1/2 tsp turmeric powder.
stir very well and saute the onions till they become translucent.
now add 2 tsp besan or gram flour.
mix the besan very well.
add 1/4 cup chopped tomatoes. adding tomatoes are optional and you can skip it. stir and saute the tomatoes for 2 minutes.
then add 1.25 to 1.5 cups water.
stir very well.
bring this mixture to a simmer. about 4 to 5 minutes on a low to medium flame.
now add the crumbled or chopped potatoes and stir very well.
cover and simmer the potato masala for 4 to 5 minutes on a low to medium flame. the potato masala should thicken and have a right consistency which is not too thick nor thin.
season with salt as per taste. mix the salt with the rest of the potato masala. you can also add a bit of sugar if you want.
lastly add 2 tbsp chopped coriander leaves. stir very well and switch off the flame.
serve potato masala with pooris or chapatis or dosa.