This may be made a day or a few days ahead, up to 10 days maximum. Soak the tamarind in 2 cups of warm water (warm water is fine, don't use boiling hot water). Set aside till required. It usually takes 5-10 minutes for the tamarind to soften enough for the juice to be extracted. Though 10 minutes is sufficient, for best results I soak the tamarind overnight. This is optional.
Meanwhile Measure out all the ingredients, checking that the spices and condiments are dry.
Roast (on a dry pan) separately, each of the ingredients listed out as "To Roast and Powder", as below.
Dry roast the methi/ fenugreek till they just begin to darken or for about 5 seconds on a hot pan kept on low flame, and transfer to a dry bowl.
Keeping the heal on low, roast the dals / lentils till they just begin to darken, for about 5 -10 seconds and transfer to the same bowl.
Roast the red chilies for about 15 seconds and transfer to the bowl.
Roast the coriander seeds for about 10 seconds, after all the above, as coriander tends to leave a residue in the pan. Transfer the coriander to the bowl, wipe out the pan to remove the residue.
Roast the sesame seeds quickly for 5-10 seconds or before they darken. Sesame can burn very fast, and sputters in the hot pan, so keep the flame on low and remove quickly. Add it to the bowl.
Let the roasted ingredients cool, and then grind to a fine powder. Set aside till required.
Extract the juice of the tamarind, by taking the ball of tamarind out of the water and squeezing out any left over juice. Strain to remove any seeds or bits of tamarind fiber from the water. Discard the fiber. If using ready made tamarind extract, use about 1 tablespoon of paste and mix it in warm water
Heat the pan/ kadai and add sesame (gingelly oil). Other oils such as sunflower oil may be used, but sesame oil will give the authentic and perfect taste. Do not however use coconut oil, mustard oil and other oils with distinctive smell and flavour.
Once the oil is hot, add the mustard seeds and let them burst. Keep the pan on low flame.Add curry leaves. If the curry leaves are fresh, stand back as they may sputter.
Add chana dal/ kadala paruppu and split urad dal, saute for 5- 10 seconds till they just begin to darken. Add hing/ asafoetida powder.
Add Turmeric powder, sauté for 5 seconds
Add Red chilies, saute for 15 seconds, stirring so the chilies do not char (blacken).Add the peanuts, saute for 20 seconds so they are fried through. Peanuts have a tendency to split and even burst when added to hot oil.Add the tamarind extract/ tamarind paste in water, to the pan of spices. Bring the sauce to a boil, add the roasted spice powder.
Lower the flame, add salt. I add only a little salt to the paste, and then add more when I'm mixing it with rice for Puliyodharai/ Tamarind rice. Keeping the stove on low flame and stirring frequently, let the paste cook.Turn off the stove when the consistency is that of a thick paste. This may take 20 minutes or more.