Heat oil in a thick bottom pan. Splutter cumin seeds and fenugreek seeds. Add curry leaves and garlic. Sauté until garlic browns lightly.
Add crushed tomato, turmeric powder, salt and black pepper powder.
Add filtered water. Give everything a nice stir.
Add rasam powder. Mix well and let the rasam come to a gentle boil. Taste for salt and tanginess (if your tomatoes are not tangy enough, you can add a dash of lime juice or dry mango powder/amchur, or a bit of tamarind juice).
Add more water if you like your rasam to be less thick.
Sprinkle finely cut cilantro, mix and serve hot. You can serve this as a soup, or pair it with rice, dal, homemade ghee and curry.
Or serve it as a hot soup (best to serve it in a stainless steel glass) with a tiny dollop of homemade ghee.