Prepare tamarind water.

In a saucepan, combine tamarind water, diced tomatoes, rasam powder, cumin powder, black pepper powder, asafoetida (hing), and curry leaves.

Add fresh thyme leaves and stir.

Bring the mixture to a boil over medium-high heat, then reduce heat and simmer until tomatoes are cooked.

Clean and wash arhar dal (split toor dal). Pressure cook with water and turmeric powder for 3-4 whistles.

Turn off the heat and allow the pressure to release naturally.

Whisk the cooked dal and set aside.

Add the dal to the tamarind-tomato base. Bring the rasam to a boil and then reduce to low flame.

Simmer the rasam for at least 5 minutes to allow the flavors of the rasam powder to meld. Adjust salt to taste and simmer for 3 more minutes before turning off the heat.

While the rasam is simmering, heat ghee in a tadka pan. Add mustard seeds and cumin seeds and allow them to splutter.

Add curry leaves to the tadka and let them crackle. Remove from heat.

Pour the tadka over the lemon thyme rasam.

Squeeze fresh lemon juice into the rasam just before serving.

Serve hot with rice and a side dish such as beetroot poriyal.