Heat a pan, add urad dal, dry red chillies and roast till dal turns golden in color. Switch off stove.
Immediately add tamarind to the pan and roast in the heat of the pan itself. Transfer to bowl to cool.
In the same pan, add white sesame seeds and dry roast over flame till you get aroma. Transfer to the same bowl.
In a saucepan, heat 1 cup water, add a pinch of salt and turmeric powder.
Tip the Vazhaipoo along with buttermilk into a colander to drain completely. Squeeze out the excess liquid and add the Vazhaipoo to the water.
Cook for 4-5 minutes till it's completely cooked. Once again tip the contents into a colander and let it cool completely.
Transfer the dry roasted ingredients into a mixie jar and grind till coarse.
Squeeze out excess water and add the cooked Vazhaipoo to the mixie jar. Add salt and grind to a fine paste adding little water.
Heat a pan with oil. Add mustard seeds and let it splutter.
Add the ground Vazhaipoo Thogayal and mix well, cooking it for less than a minute over low flame.
Transfer to a serving bowl.
Serve vazhaipoo thogayal mixed with rice to which a dash of ghee or sesame oil has been added or serve as a side dish with sambar or rasam rice. It goes well with idli and dosa too.