FOR THE DAL:
1 cup toor dal (split yellow pigeon peas)
2 Roma tomatoes, roughly chopped
1/4 teaspoon ground turmeric
1/2 teaspoon kosher salt
1/4 cup raw whole peanuts
FOR THE TEMPERING
1/4 cup/55 grams ghee
1 sprig fresh curry leaves
3 small pieces Indian cinnamon or 1 cinnamon stick
3 red dried chiles, such as chile de árbol
1/4 teaspoon black mustard seeds
Pinch of asafoetida
Prepare the dal: Soak the pigeon peas in a large bowl of warm water for about 1 hour. (They will have swelled a little.) Thoroughly rinse the soaked pigeon peas with fresh water, then tip the drained pigeon peas into a pot.
Add tomatoes, turmeric, salt and 5 cups water, and bring to a boil over high. Reduce the heat to medium and simmer until very tender, 25 to 30 minutes.
Use an immersion blender to purée some of the dal, leaving some intact and getting some very smooth, or whisk vigorously to break up some of the soft dal. Stir in the peanuts and continue to simmer, stirring occasionally, until the dal is very tender, about 30 minutes. Taste and adjust with salt. If the dal has become too thick for your liking, stir in a splash of water.
Prepare the tempering: In a small saucepan over medium heat, warm the ghee. When hot, carefully add all of the tempering ingredients (the mustard seeds will sputter!) and swirl the pan until you can smell all the toasted spices, about 30 seconds. Pour everything over the hot dal.