Cut watermelon into pieces, remove seeds, and puree in a blender.

Strain the watermelon puree to extract the juice.

Soak tamarind in water and extract the juice.

Wash and pressure cook the arhar dal with water for 3 whistles.

Allow the pressure to release naturally.

Mash the cooked dal completely.

Combine tamarind juice and watermelon juice in a bowl.

Add crushed garlic, pepper, and cumin mixture to the juice.

Add turmeric powder, chili powder, rasam powder, asafoetida, and salt.

Mix well and pour the mixture into the cooked dal in a pan.

Boil on medium flame, adding water if needed.

Heat ghee in a separate pan for tempering.

Add mustard seeds and curry leaves to the hot ghee until they splutter.

Pour the tempering over the boiling rasam.

Simmer until rasam becomes frothy.

Remove from heat and squeeze in lemon juice.

Garnish with coriander leaves and serve hot.