Soak 2 tbsp tamarind in 1 cup warm water and extract the juice
Crush 1 tsp black pepper, 1 tsp cumin seeds, 3 garlic cloves, and a few curry leaves
Heat 1 tsp ghee or oil in a pan
Add 1/2 tsp mustard seeds and let them splutter
Add 1/2 tsp cumin seeds, a pinch of asafoetida, and a few curry leaves
Add the crushed pepper-cumin-garlic mixture
Add 1 chopped tomato and cook until soft
Add 2 to 3 cups water
Add the tamarind juice
Add salt to taste
Add 1/2 tsp turmeric powder
Add 1 tsp rasam powder
Simmer for 5 to 7 minutes without boiling too long
Add chopped coriander leaves
Serve hot with rice or drink as soup