dry roast sesame seeds on medium-low heat until golden brown. Take off the heat and let them cool completely. Blend in short pulses until the mixture is coarsely ground.
In a small bowl, combine tamarind paste and ½ cup water. Stir in onions, green onions, salt, sugar and roasted sesame powder. Using clean hands, mix all the ingredients well for about 1~2 minutes. Stir in another 1 cup water and mix again. Taste and add more tamarind, salt, green chilies to adjust the seasoning.
Heat oil in a small pan. Add mustard, cumin seeds and once the seeds start to splutter, add curry leaves and cook for 30 seconds. Add the tempering into the pulusu and mix well. Serve with rice and dal.
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Notes
You can use either store bought tamarind paste/ pulp or dry version available as bricks. If using the dry tamarind, soak a small lemon size piece in warm water for 15 minutes, then squeeze out the pulp.
Substitute medium size shallot for the red onion.
Make sure not to process the roasted sesame seeds for too long. The mixture will get clumpy and pasty. Blend in short pulses until the mixture is coarsely ground.