In a medium saucepan, add 1 tsp oil. When the oil is hot, add cumin seeds and cook until it turns brown.
Add the dried neem flowers and sauté for a couple of seconds.
Make a tamarind paste by adding a large piece of dry tamarind to 2 cups of lukewarm water. Optionally, you can substitute with 1 tbsp store-bought tamarind paste and 2 cups of water.
Add the smashed ginger, sliced green chilli, salt, turmeric and rasam powder.
Strain the pulpy tamarind water into the pan. Let this broth boil for 10-15 mins.
In a separate small pan, add 1 tbsp ghee/oil. Add the mustard seeds. When they start popping, add the curry leaves. Pour this immediately on top of the rasam.
Finish by adding jaggery. Garnish with chopped cilantro.