Take peanuts in a pan and dry roast them still they shed their skin off. It may take few minutes. Let it cool down, then crush them between your palm to remove the skin off.
Heat a pan adding oil, onion, red chillies and garlic cloves. Roast them in medium flame and switch off.
Add roasted onion, garlic, red chillies, peanuts, cumin, salt and tamarind in a mixer and grind them together to little coarse puree. Add water as needed.
Yummy peanut onion chutney is ready to serve with dosa and idli.