Wash the tur dal well. Soak the dal in water for 30 minutes.
Pressure cook the dal with the green chilli, turmeric and ginger along with 2 cups water. [Watch : How to pressure cook dal]
Meanwhile, in a small pan, dry roast the peppercorns, cumin seeds and red chillies for 5-6 minutes on a low heat, until aromatic. Wait for it to cool. Crush it to a coarse powder using a mortar-pestle or in the spice grinder.
Once the pressure cooker has cooled, open the lid, discard the green chilli and puree the dal with the turmeric and ginger, using a stick blender or the mixer.
Return this to a pan, add around 3/4 cup of water. Bring this to a simmer on a medium heat. Add the turmeric paste spice powder, salt, give it a good stir and allow this to simmer for 3-4 minutes, until it starts foaming on the surface. Remove this from flame.
In a small tempering ladle / pan, heat ghee. Add the cumin seeds and curry leaves. Once the seeds splutter, transfer this over the rasam and keep covered until ready to serve.