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 usli.
In a kadai/pan, heat oil. Add mustard seeds, urad dal, channa dal. Let they splutter and turn golden.Add few curry leaves,red chilly broken.
Add finely chopped onions and green chillies . Saute 2-3 mins. Let onions get translucent.
Next add in the cooked horse gram, sugar ,salt to taste . Mix . Cover and cook for 2-3 mins. Let horsegram take in flavors and salt.