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.
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.
Roast the methi/ fenugreek for about 10 seconds on a hot pan, and transfer to a dry bowl.
Roast the dhals for about 10 seconds and transfer to the same bow.
Roast the red chillies for about 20 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.
Roast the sesame seeds quickly for 10 seconds or before they darken. Sesame can burn very fast, and splutters in the hot pan, so keep the flame on low and remove quickly. Add it to the pan.
Let the roasted ingredients cool, and then grind to a fine powder. Set aside till required.
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 taste. Do not however use coconut oil, mustard oil and other oils with distinctive smell and flavour.
When 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 splutter.
Add Chana dhal and split uradh dhal, saute for 10 seconds.
Add Turmeric powder, sauté for 5 seconds
Add Red chillies, saute for 20 seconds, stirring so the chillies do not char (blacken).
Add the peanuts, saute for 20 seconds. Peanuts have a tendency to burst when added to hot oil.
Meanwhile, 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 fibre from the water. Discard the fibre.
Add the tamarind water/ extract to the pan of spices. If using readymade tamarind extract, use about 1 tablespoon of paste and mix in warm water.
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 with rice for Puliyodharai.
Turn off the stove when the consistency is that of a thick paste.