To begin making the Chettinad Style Kara Kuzhambu Recipe, we will first make the masala. 

Heat a small pan on medium heat; add fenugreek seeds, coriander seeds, fennel seeds, red chillies. Roast these spices until the aroma wafts in the air. Stir in the freshly grated coconut and roast for another 2 to 3 minutes. 

Turn off the heat and allow the spices to cool. Transfer the spices into a mixer jar, add 1/2 cup warm water and grind to make a smooth paste.

To cook the kara kuzhambu, heat oil in a pressure cooker over medium heat; add the onion, garlic and saute for a few minutes until the onion softens. Add the chopped tomatoes and saute until the tomatoes are mushy.

Stir in the potatoes, brinjal, jaggery, tamarind water, sambar powder and salt. Pressure cook for 3 to whistles and turn off the heat and allow the pressure to release naturally.

In the meantime, make the seasoning; heat oil in a tadka pan; add the mustard seeds and curry leaves and allow it to crackle. Turn off the heat and keep aside. 

Once the pressure releases, stir in the coconut mixture, the seasoning mixture and give the Chetinnad Kara Kuzhambu a brisk boil for 3 to 4 minutes. Check the salt and adjust according to taste.

Serve hot Chettinadu Style Potato Kaarakozhambu along with Steamed Rice, Beetroot Thoran and Elai Vadam for a weekday meal.