Soak tamarind in hot water for 15 minutes, then extract juice and strain.
Heat gingelly oil in a heavy-bottomed pan over medium heat.
Add mustard seeds and let them splutter, then add fenugreek seeds and curry leaves.
Add chopped onion and pearl onions, sauté until golden brown.
Add chopped garlic and cook for 2 minutes until fragrant.
Add chopped brinjals and cook for 5-7 minutes until slightly tender.
Add chopped tomato and cook until it breaks down and becomes mushy.
Pour in tamarind juice, add sambar powder, turmeric powder, and salt.
Bring to a boil, then reduce heat and simmer for 15-20 minutes until the kuzhambu thickens.
Adjust salt and spice levels as needed, then remove from heat.