rinse the dal well. pressure cook the dal with the tomatoes, garlic, ginger and a pinch of turmeric powder, 2.5 cups water for 7-8 whistles or more till the lentils are cooked and mushy.
squeeze the pulp from the tamarind directly into its bowl of water. when the pressure settles down on its own, open the lid.
mash the dal with a madani, wooden spoon or hand blender till smooth.
strain the tamarind pulp and add to the dal.
also add the green chilies, turmeric, red chili and coriander powder. stir in the ¾ or 1 cup water along with salt.
keep the dal on a low flame and simmer for 8-10 minutes till the raw aroma of the tamarind goes away and the all the flavors have blended well and the dal has reached a medium consistency.
cover and keep the cooked dal aside.
preparing the tempering
heat oil in a small frying pan. crackle the cumin seeds first.
then add the garlic and fry for 4-5 seconds. add the dry red chilies, curry leaves and asafoetida.
fry till the red chilies change their color and the curry leaves become crisp.
pour this tempering and stir.
cover and keep aside the khatti dal for 5-6 minutes for the flavors to mingle.
serve khatti dal with steamed basmati rice or jeera rice or roti.
For cooking the lentils in a pot - rinse and soak the lentils for atleast an hour. boil 3-4 cups water with a pinch of turmeric. add the drained lentils. whilst cooking remove the scum with a spoon. cook the lentils till the each lentils has become soft and mushy. add more hot water if required while cooking. once the lentils are cooked, you can the tomatoes, etc and simmer till the tomatoes are cooked and then proceed with the recipe.