Dry roast all the ingredients on medium flame until aromatic. Keep aside and allow it to cool.
Grind these spices into a fine powder with the help of a mortar or a blender. Your Sambar powder is ready; you can make extra powder and store it in a jar for later use.
Pressure cook the Toor Dal with salt and turmeric powder for 3-4 whistles.
After the dal is fully cooked, mash it with a masher or ladle.
In a deep pan, heat oil and saute onions till translucent. Now add all other vegetables and saute for 2 minutes.
Add chili powder and stir for one minute. To this, add 5 cups of water, tamarind paste, sambar powder, and jaggery. Let it boil for 2-3 minutes.
Check if all the vegetables are cooked; now add the mashed dal and stir it.
Add coriander leaves and let the dal simmer for 5 minutes.
In a small pan, heat oil and add mustard seeds, cumin, fenugreek seeds, asafoetida, and curry leaves.
After the spices pop and the curry leaves are crisp, transfer this tempering into the sambar dal pan.
Sambar is ready to be served with idli, dosa, uttapam, or rice.