Cut tips of the onions and soak them in plain water for 10-15 mins. Peel them later. It will be easier to peel.
To a mixer jar - add small onion, red chillies, tamarind, jaggery and salt to taste.
Grind it to a paste without adding water. No need to make super smooth.Set aside.
Heat gingelly oil in a kadai.Add mustard seeds let it splutter.Then add curry leaves, pinch of hing and haldi.Don't skip hing and sesame oil .. they enhance taste.
Add ground Onion paste to it.
Combine everything nicely.
Keep stirring the thokku in between so that it doesn't get burnt . Let the raw smell go and thokku thickens & nice texture. Taste test. If you need add chilli powder / salt. If it is dry,add few more tsps of oil.
After some 10-12 mins, you will notice that thokku has turned deep brown in color .The moisture content has evaporated ,oil starts leaving the sides and it comes off the edges as a mass.Switch off the stove .
That's it our spicy Onion thokku is ready to enjoy. Store in air tight jar once its cooled to room temperature. Stays good for about 3-4 days without fridge and if refrigerated remains good for months . Tastes awesome with idli , dosa, chapathi , plain rice, curd rice etc.