Tender lentils slow-simmered with warming turmeric, finished with a sizzling tarka of golden ghee, roasted cumin, and fresh coriander.
Pressure-cook the toor dal with 1 cup water until soft and whisk it smooth.
Coarsely crush the peppercorns, cumin seeds, and garlic cloves.
Boil the tomatoes with 2 cups water, the crushed masala, and salt until the tomatoes turn pulpy, then add the dal and simmer until frothy.
Heat ghee, pop the mustard seeds and curry leaves, and pour into the rasam.
Rest 10 minutes and serve hot as a soup or with fried medu vadas.