Heat oil in a pan and add the garlic cloves. Saute for about 2 minutes until the raw smell goes and the garlic turns lightly golden.
Add the whole sambhar onions (or roughly chopped regular onion). Saute until the onions turn soft and glossy.
Add the broken dry red chillies and sauté for a few seconds.
Add a small piece of tamarind and mix well. Switch off the heat and allow the mixture to cool completely.
Transfer the cooled mixture to a blender. Add salt, hing, and coriander leaves (if using).
Grind to a smooth or slightly coarse chutney, adding water little by little to adjust the consistency.
Heat oil in a small pan for tempering. Add mustard seeds, dry red chilli, and curry leaves.
Pour the tempering over the chutney, mix well, and serve fresh.