Cook toor dal with turmeric. Cook potato, tomato and onion separately, I mean do not mix them with dal while cooking. (If you have the cooker vessels, use the down one for the dal and the upper one for vegetables. This way the dal cooks faster than the vegetables). Around 3-4 whistles are enough in cooker. (If using microwave, cook both separately one after the other).

Mash the dal with a spoon. Add the vegetables to dal and add sufficient water (this sambar tastes good when the dal is cooked well and mashed well).

Heat the dal, vegetables mixture. Add salt. When it starts boiling, add the sambar powder (Do not hold the entire packet of sambar powder on boiling sambar. The steam gets into the packet and the powder gets spoiled. So use spoon to take out the powder away from the boiling sambar and then add the powder). Add the chopped coriander leaves and cook for 2-3mins.

Heat oil and add mustard seeds. When they start popping, add asafoetida and curry leaves (tear the curry leaves into two to increase the aroma). Add this seasoning to Sambar and immediately close the lid.