Madhur Jaffrey's version of this classic. From the preface to the recipe, she says "This delicious dal curry may also be made with moong dal or an equal mixture of red lentils, masoor dal, and moong dal. Serve with rice and fish. —JohnL
masoor dal (red lentils), washed and drained
Put the dal and 3 cups water in a medium pan (John's note: I like to make this in my 2-qt Le Creuset round dutch oven). Bring to a boil but do not let it boil over. Skim off the froth and add the turmeric. Stir, cover partially, turn heat to very low (John's note: on my stove very low is too low, so I use med-low to ensure the dal will simmer merrily) and simmer gently for 40 minutes. (John's note: toward the end of the cooking time, stir and make sure it doesn't threaten to boil dry. But you want most of the water to have been absorbed). Add the tomatoes, cilantro, salt, and cayenne, bring to a simmer , cover and simmer 10 minutes over low heat. Stir and turn off the heat.
Pour the oil into a small pan or small frying pan and set over medium-high heat. When hot, put in the mustard and cumin seeds. As soon as the mustard seeds begin to pop, a matter of seconds, add the onions and curry leaves (John's note: I've made this with and without the curry leaves, and I like it either way, but prefer it without curry leaves--they add a pervasive flavor). Stir and fry until the onions start to brown. Now put in the ginger and garlic. Stir for a minute and then empty the contents of the small pan into the pan with the dal. Stir to mix.