Take 2 1/2 cups water in a vessel. Add mashed tomato, 1 teaspoon tamarind extract, turmeric powder, asafoetida and curry leaves. Mix well and add salt.
Cook this medium flame for 5-7 minutes.
Add the betal leaves mixture and mix well. Simmer till the rasam starts to froth. Once the rasam is frothy switch off the flame. Heat 2 teaspoons ghee in a small pan and temper with mustard seeds, red chili and curry leaves. Add this tempering along with ghee to the rasam. Mix well, add cilantro leaves and serve vetrilai rasam hot.
Notes
1. You can mash 2 teaspoons cooked toor dal and add in the rasam 2. Garlic is optional