Boil chopped tomatoes with tamarind paste, salt, and water until soft, then mash well.
Crush cumin seeds and garlic paste together, add along with black pepper powder to the tomato broth.
Simmer gently for 8 minutes without letting it boil hard.
Heat ghee in a small pan, crackle mustard seeds, curry leaves, and asafoetida; pour into rasam and serve piping hot.