Dry roast the sesame seeds on medium heat 2 to 3 minutes, stirring, until a few seeds pop and they smell nutty. They should stay light. Tip onto a plate to cool 5 to 10 minutes.
In the same pan, toast the dry red chillies 20 to 30 seconds until they darken slightly. Cool.
Grind
Add cooled sesame, chillies, garlic, tamarind, jaggery, roasted cumin, and salt to the blender. Pulse to a coarse powder.
Add 2 tablespoons water. Blend to a thick paste. Add the last tablespoon, or more by the teaspoon, until it is spoonable. Taste for salt and jaggery.
Notes
Cool the seeds fully. Warm seeds turn oily and bitter in the jar.If the chutney tastes bitter, the roast went too long. Start over. Extra jaggery only hides a mild roast, not a burnt one.Optional tadka: 1 teaspoon oil, mustard seeds, curry leaves. I skip it on rotlo nights so the til stays the main taste.Store in an airtight container in the refrigerator for up to 7 days. It firms up. Loosen with a teaspoon of water.A half-cup batch is the right size. Double only if you will eat it this week. Sesame goes stale in the fridge after that.