Dal Shorva (creamy lentil soup with caramelized onion)

This recipe is also from Williams Sonoma's "Savoring India" (I love this cookbook).
You can probably find red lentils in any place that carries Middle Eastern or Indian food. If unavailable, you can use yellow split peas, but you will need to cook them longer (40-60 minutes, or until tender), and they will have a different flavor.

1 1/2 cups red lentils
4 cups chicken stock or water
1/2 tsp ground turmeric
1-inch piece fresh ginger, peeled and chopped
2 tomatoes, chopped
1 cup milk
1 1/2 tsp salt, or to taste

Garnish:
1/4 cup unsalted butter
1 yellow onion, finely shredded
1 tsp cumin seeds
ground black pepper to taste
1/4 cup chopped fresh cilantro (optional)

Pick over the lentils, removing any stones or misshapen or discolored lentils. Rinse thoroughly and place in a deep pot. Add the chicken stock or water, turmeric, ginger, and tomatoes and bring to a boil. Reduce the heat to low and simmer, uncovered, until the lentils are soft, about 25 minutes.

Remove the heat and, working in batches, puree in a food processor or blender until smooth (I use an immersion blender). Return the soup to the pot, stir in the milk and salt, and heat until piping hot. Simmer gently over low heat while you make the garnish.

To make the garnish, in a frying pan over high heat, melt the butter. Add the onion and cumin and cook, stirring occasionally, until the onion is brown, about 5 minutes. (I find it takes longer than this, so I usually do this step while the lentils are cooking)

To serve, ladle the soup into warmed bowls and sprinkle generously with black pepper. Divide the onion-butter mixture among the bowls, sprinkle with cilantro if desired, and serve at once.