1 tbsp of tamarind extract mixed with 1 cup of water. Alternately, if you're using tamarind pods, soak a 1-inch ball of the pods in warm water for 15 minutes, then extract the flavor by crushing the pods with your fingers. Discard the solids and reserve the liquid portion.
½ tsp turmeric
3 tsp vegetable oil
2 tbsp coriander seeds
2 dry red chillies
1 tbsp chana dal or bengal gram dal
¼ tsp dry fenugreek seeds (methi)
2 cups red pearl onions, ends trimmed and papery skins peeled. Tamil cooks sometimes soak the onions overnight which makes it easier to slip the skins off.
1 sprig of curry leaves (about 12 individual leaves)
1 tsp mustard seeds
A generous pinch of hing or asafetida
Salt to taste
Mix the lentils and turmeric, add water and cook until tender in a pressure cooker. Or cover the peas with an inch of water in a pot and bring to a boil, then slap on a lid, lower to simmer, and boil for 30-45 minutes or until the peas are tender enough to mash. Add more water if needed as they cook.
Prepare the ground masala by heating 1 tsp of oil. Add to it the coriander seeds, chana dal, fenugreek seeds and chillies and saute until the coriander seeds and dal turn a few shades darker and are lightly golden-brown. Remove to a blender, add enough water to keep the blades moving, and process to a smooth paste.
Heat 1 tsp of the oil, add the pearl onions and stir-fry until the start to turn golden. Add the tamarind extract and let the mixture cook about 8 minutes.
Add the ground masala and stir well to mix. Add the cooked tuvar dal and bring everything to a boil.
Lower the heat to a simmer, add salt to taste, and let the sambar cook for 10 minutes so all the flavors have a chance to meld together.
To temper the sambar-- an important flavor-building step-- heat the last teaspoon of oil in a small saucepan and add the mustard seeds. When they crackle, add the asafetida and curry leaves. Fry for a few seconds, turn off the heat, and pour over the sambar. Mix well.
Recipe by Holy Cow! at http://holycowvegan.net/2014/02/onion-sambar-vengaya-sambar.html