Rinse the toor dal thoroughly under running water.In a pressure cooker, add the rinsed dal, 3 cups of water, and turmeric powder.
Cook on medium heat for 3-4 whistles or until the dal is soft and mushy. If using a pot, cook until the dal is tender, which may take 30-40 minutes.
Soak tamarind pulp in 1/2 cup of warm water for 10 minutes. Mash the tamarind to extract its juice and strain to remove any fibers or seeds.
Transfer the cooked dal to a large pot. Add the tamarind extract, red chili powder, coriander powder, and salt.
Simmer the mixture on low heat for 10-15 minutes, stirring occasionally to prevent sticking.
Prepare the Tempering: Heat ghee in a small pan. Add mustard seeds and let them splutter. Add cumin seeds, dried red chilies, curry leaves.
Pour this tempering over the simmering dal and mix well.
Mix the tadka into dal.
Garnish the dal with freshly chopped coriander leaves.
Khatti dal is ready. to. Serve hot with steamed rice, papad, or parathas.