The many dals of India (this one, typical of the south, is from Samia Ahad, who teaches Indian cooking in New York) differ not only in the lentil used but in the tarka—literally, "seasoning with oil".
FOR THE DAL:
1/2 lb. imported red lentils (split), picked over and rinsed
1 small yellow onion, peeled and thinly sliced
1 clove garlic, peeled and minced
1/2'' piece ginger, peeled and minced
2 tbsp. fresh lemon juice
FOR THE TARKA:
2 tbsp. canola oil
1 tsp. black mustard seeds
3 dried red chiles
6–8 fresh or dried curry leaves
1. Place lentils in a saucepan with onions, garlic, ginger, and 2 cups of water. Bring to a boil over high heat.
2. Reduce heat to medium-low, partially cover, and simmer, stirring occasionally, until lentils are tender, about 25 minutes. Transfer to a food mill or food processor and purée, then transfer to a clean saucepan.
3. Add 1 cup water and lemon juice, season with salt, then bring to a simmer over medium heat. Cook, stirring occasionally, until dal is the consistency of thick soup, about 20 minutes. (If thick, add more water; if thin, simmer longer.)
4. Just before serving, prepare tarka: Heat oil in a small skillet over medium-high heat. Add mustard seeds, chiles, and curry leaves. Fry until fragrant, about 1 minute. Transfer dal to 4 bowls, season with spiced oil, and serve with rice.