Pressure cook yellow lentils with water and salt until completely soft; whisk smooth.
Boil drumstick pieces and chopped tomato in water with tamarind paste and sambar powder until tender.
Combine cooked lentils and vegetable broth, simmering together for 10 minutes.
Heat ghee in a small pan, crackle mustard seeds, curry leaves, and asafoetida.
Pour tempering into sambar, mix well, and serve hot with idli or rice.