To begin, dry roast the dal on medium heat until it colorizes. Allow it to cool. Grind into a coarse powder and keep aside.
Heat mustard oil in a pan to smoking point and let it cool a bit. Add the cumin seeds, mustard seeds, and asafoetida. Allow them to crackle.
Add the chopped onions with green chillies. Saute until the onions are translucent.
Add the ginger garlic paste and saute for a minute.
Next, add the tomatoes with salt. Cook until they soften and oil starts appearing on the sides.
Now add the ground dal and saute until you can smell the aroma.
Add about 3 cups of water in batches to avoid forming lumps. Mix well.
Add the dry masalas - Kashmiri red chilli powder, turmeric powder, coriander powder, and cumin powder. Mix well.
Allow it to come to a boil. Reduce the heat and let it cook on medium to low heat for 15-20 minutes until the dal is done and it thickens. Or you can pressure cook it on medium heat for 3-4 whistles.
Finish with chopped green coriander leaves and mix well.
The Urad Dal Chainsoo is ready to serve. Serve hot with rice.