Rinse the toor dal and drain the water. Pressure cook the toor dal by adding 1 cup of water and 1/4 tsp of turmeric powder for 3 to 4 whistles. Let it cool and mash it and set it aside.
You can also cook in Instant Pot. As it's 1/4 cup of toor dal, you can use a PIP method and cook the toor dal for 20 to 25 minutes at high-pressure mode and release the pressure naturally.
Roast and grind the masala-
Heat 1/2 tsp of oil in a pan and when the oil is hot, add the coriander seeds, chana dal, dried red chilies, mustard seeds if using and the shallot.
Dry roast it until you get the aroma of the coriander seeds. Now add the coconut and roast for 30 seconds and turn off the heat. Let this mixture cool.
Transfer these roasted spices along with the coconut into a mixer jar and grind into a smooth paste by adding 3/4 to 1 cup of water.
Now add this ground mixture to the cooked dal. Rinse the mixer jar with 1/4 cup of water and add that water as well to the dal. Mix the dal and the ground paste together and set it aside.
Prepare the sambar-
Take a saucepan or kadai with a heavy bottom, heat 1.5 tbsp oil. I used my uruli vessel for the sambar.
When the oil is hot, add the mustard seeds and fenugreek seeds. You can add few curry leaves at this stage, but we did not add any.
When the mustard seeds splutter, add the shallots and saute for 2 minutes. Then add 1/2 cup of water and cover and cook for 3 to 5 minutes until the shallots are tender.
Now mix the tamarind paste with 1.25 cups of water and add it to the shallots. Add the salt as well and bring this to a boil.
Add the sambar powder and mix well without any lumps. Let it cook for 3 minutes.
Now add the dal and spice paste mix and jaggery to the sambar and mix thoroughly.
Reduce the heat to medium-low and bring it to a gentle boil. The sambar will become frothy, and when it starts to boil, turn off the heat. Now add the curry leaves and cover the sambar partially. Let the flavor infuse.
As this is an exclusive onion sambar, I did not add any other veggies. But you can always add either okra or drumstick or brinjal. They go very well in this sambar.
Instead of shallots, you can use regular big onions as well. In that case, while grinding add 1 tbsp of chopped onion. If you are using regular onions, chop them roughly into wedges or big chunks. Do not chop them finely.
Check the consistency of the sambar towards the end and adjust the water accordingly. If the kuzhambu is thick, then add 1/2 more cup of water and simmer for 2 to 3 minutes. If sambar is thin in consistency, mix 1/2 tsp of rice flour with 2 tbsp of water and add it to the sambar. Bring it to a boil and turn off the heat.
As always, adjust salt and spice according to your preference. The same goes for tamarind also.
I have explained about tamarind in my vathal kuzhambu post. The tamarind you use plays a significant role. The age of the tamarind determines the tanginess and the color of the sambar. So adjust the tamarind according to the variety you have.
You can add 1/8 tsp of asafoetida. We don't add cilantro to sambar and also ginger-garlic paste. Jaggery is optional.
I recommend adding coconut oil for this recipe. But you can add any other oil of your choice.