Indian Potato and Chickpea Soup

I got this recipe from cooking.com. It's a real nice, down to earth, hearty soup. It's easy to make and easy to eat. The popping mustard seeds are fun. It must be something about Denver, but I always have to cook soups like this longer so that the potatoes get soft. I usually substitute olive oil for the butter, but either way it tastes great.

Ingredients

2 tablespoons unsalted butter
1 teaspoon mustard seeds
1 small serrano chili, sliced lengthwise
4 cloves garlic, minced
1 small onion, diced
1/2 teaspoon ground coriander
1/4 teaspoon turmeric
2 teaspoons kosher salt
1 vine-ripe tomato, diced
1 15.5-ounce can chickpeas, drained and rinsed
1 1/4 pounds Yukon Gold potatoes, cubed 1 inch
4 cups water
2 tablespoons freshly squeezed lime juice
1/4 cup chopped fresh cilantro

Directions

Heat the butter in a Dutch oven or large soup pot over medium-high heat. When the foam subsides, add the mustard seeds. Heat until they pop, 30 seconds to 2 minutes, depending on the age of your seeds. Add the chili, garlic and onion and cook until softening, 1 to 2 minutes. Sprinkle in the coriander, turmeric and salt; stir for 30 seconds. Add the tomato and stir to break down, about 2 minutes. Pour in the chickpeas, potatoes and water. Bring to a boil and then simmer until the potatoes are tender, about 12 minutes. Turn off the heat and stir in the lime juice. Ladle the soup into bowls and garnish with cilantro.