Clean , Wash horse gram and pressure cook with 6 cups of water in the cooker for 3 whistles on high.Reduce the flame to sim and let it cook for another 2-3 whistles.If you are soaking the horse gram for 3-4 hours and later pressure cooking, then 3-4 whistles on high is enough.
Let the cooker cool and pressure release naturally. Check if horsegram is well cooked. It must be soft when pressed yet retain shape.
Drain the cooked horsegram using a colander. Save the broth for making rasam. Keep aside horsegram to make a stir fry later.
Add slit green chillies to the horsegram broth.Keep on flame for boil.
Grind and prepare masala. In a blender take a ladle of cooked horsegram,coconut , diced onion , rasam powder , salt and tamarind . Add little water and make a smooth paste.
Add ground masala to horsegram broth. Mix well and add water to get the desired consistency.
Simmer and boil well for 8-10 mins till raw smell goes. Add few curry leaves and chopped coriander leaves .
Finally, make a tempering . Heat ghee.Add mustard seeds and garlic pieces. When they splutter , add asafoetida, Pour this to the hot rasam and close the vessel with a plate immediately. Let the flavors of tempering get trapped inside the rasam and become more flavourful.
Serve hot with rice. If there is leftover rasam, strain it the next day in a mesh strainer and slightly heat it and serve as a nice warm broth. It tastes so yum the next day.