Whisk yogurt, salt, and water in a bowl.

Peel the outer skin of the plantain stem and discard it. Chop the stem and place it in the yogurt water to prevent discoloration.

Preheat the pressure cooker over medium heat.

Add mustard seeds and cumin seeds; allow them to crackle.

Add ginger, garlic, asafoetida, and curry leaves; stir for a few seconds.

Add the banana stem along with the yogurt water, tomatoes, coriander powder, cumin powder, turmeric powder, red chilli powder, and salt.

Stir, cover the pressure cooker, and cook for about 3 whistles. Turn off the heat.

Release the pressure immediately.

Open the cooker and stir in the cooked dal and lemon juice. Add water, salt, and chilli if needed.

Bring the rasam to a brisk boil and allow it to froth up (4-5 minutes).

Turn off the heat and stir in the chopped coriander leaves.

Serve with steamed rice.