Pressure cook the arhar dal with turmeric powder, salt, and water for 5 whistles until the dal is cooked.

Mash the cooked toor dal and set aside.

Add oil to a pressure cooker and add the pearl onions.

Roast the pearl onions for 4-5 minutes until fragrant.

Add tomatoes, sambar powder, salt, turmeric powder, and tamarind water to the pressure cooker.

Pressure cook the Vengaya Sambar masala for 2 whistles and then turn off the heat.

Allow the pressure to release naturally.

Open the cooker and add the mashed toor dal and mix well.

Adjust the salt to taste.

Heat oil in a small tadka pan for tempering.

Add mustard seeds, fenugreek seeds, dry red chili, and hing and let them crackle.

Add curry leaves and turn off the heat.

Pour the tempering over the onion sambar and bring to a boil.

Stir in the chopped coriander leaves.

Transfer the Onion Sambar to a serving bowl.