Vatha Kuzhambu refers to a group of dishes cooked in tamarind paste. The cuisine emanates from Thamizhnadu and Palakkad. There are, however, some differences. In Palakkad, sun-dried vegetables are used in this curry whereas Thamizhnadu uses fresh vegetables. However, there is no hard and fast rule about this.
This dish is so integrated into the psyche of the populace of these states/regions. My sister-in-law once observed that anyone who has not tasted a vatha kuzhambu has not really lived life in full. I only mention that to emphasise how integral this dish is to the people of Thamizhnadu and Palakkad.
In this post, I have used shallots in tamarind curry. This is how it is traditionally done. However, my nephew once made this dish using the larger red onion. It tasted equally good. So, if you do not have shallots (pearl onions) readily available, use the larger red onions (sliced).

Ingredients
15-20 shallots (either whole or chopped)
1 lemon sized ball of tamarind
1 1/2 tbsp sambar powder (recipe in this blog under “Chutneys & Powders”)
A pinch of turmeric powder (haldi, manjal podi)
1 tsp date paste
Salt to taste
To Temper
1 tsp mustard seeds (sarson, kadugu)
1/2 tsp fenugreek seeds (methi dhana, venthiyam)
1 sprig curry leaves
Method
Soak the tamarind in warm water for 15 minutes
Extract the juice and discard the pulp
Set aside
Heat a wok and add the shallots
Sauté till the shallots are translucent
Add sambar powder and continue to sauté for a minute more
Add salt, turmeric powder and tamarind extract
Boil for about 7-8 minutes (add a little water if the consistency is too thick)
Add date paste and mix well
Remove from flame and transfer to a serving bowl
Heat a wok and add mustard and fenugreek seeds
When the mustard seeds begin to splutter, add the curry leaves
Roast for a few seconds and remove from flame
Add this to the vatha kuzhambu
Serve hot with red/brown rice
Enjoy!