To begin, soak the tamarind in 1 cup of warm water for about 10 minutes. Once softened, squeeze the tamarind to extract the juice, straining it to remove seeds and fibre. If using tamarind paste, dilute 2 tablespoons in 1 cup of water. Set aside.

In a medium sized pot, add the tamarind water, chopped tomato, turmeric powder, rasam powder, and a pinch of salt. Bring the mixture to a gentle simmer over medium heat, allowing the flavors to meld together for about 10 minutes. The tomato should soften and break down during this time.

Meanwhile, in a separate bowl, mix the cooked and mashed toor dal with 1 cup of water to form a smooth consistency. The lentils add thickness and depth to the rasam. Set this mixture aside to add later.

In a mortar and pestle, coarsely crush the black peppercorns and cumin seeds together. This freshly ground spice mix will provide a robust flavour and a slight heat to the soup.

Once the tamarind and tomato mixture has simmered for 10 minutes, add the crushed pepper-cumin mix along with the mashed dal mixture. Stir everything well and let the rasam come to a boil. Simmer for an additional 5-7 minutes, adjusting the salt to taste.

In a small tempering pan, heat 1 tablespoon of ghee or oil over medium heat. Add the mustard seeds, allowing them to crackle. Next, add the dried red chilies, crushed garlic, and curry leaves. Sauté for 30-40 seconds, just until the garlic turns golden and fragrant.

Pour the tempering (tadka) over the simmering rasam. Stir it well and let the soup simmer for another 2 minutes. The tadka adds a burst of flavour and aroma, enhancing the overall taste of the dish.

Remove the rasam from heat and garnish with freshly chopped coriander leaves. Serve hot with steamed rice or enjoy it as a flavourful, warming soup. For extra heat, you can add a touch of freshly ground black pepper before serving.