Make the soup: Heat a small, dry sauté pan over medium-high heat. When the pan is hot, add the coriander seeds and toast them-stir constantly (or shake the pan gently) to keep the seeds from burning-until they darken slightly and become very fragrant, 1 to 2 minutes. Immediately transfer them to a dish and set aside. Return the sauté pan to the heat; add the pepper-corns and toast, shaking the pan, for about 2 minutes. Pour onto the plate with the coriander seeds. Put the toasted coriander and pepper in a spice grinder or mortar and pestle and grind to a fine powder.
In a large (at least 4-quart) saucepan, combine the lentils, onion, celery, carrot, garlic, ginger, chile, cheesecloth-wrapped cilantro sprigs, and 2 tsp. salt with 2-1/2 quarts water. Bring to a boil over medium-high heat. Reduce the heat to medium low and simmer for 30 minutes. Remove the cilantro sprigs. Add the ground coriander and pepper to the soup and simmer for another 10 minutes. Purée the soup using a hand blender or a regular blender until the soup is very smooth. Strain the purée through a medium sieve into a large serving bowl. The soup can be made to this point one day ahead; reheat it gently before continuing.
Make the tarka and garnish the soup: Set a small deep saucepan over medium heat and add the canola oil. When the oil is shimmering, add the mustard seeds and cook, uncovered, until they pop, 30 to 60 seconds. Add the cumin seeds and cook for another 1 minute. Quickly but carefully, pour the hot tarka over the soup and mix well. Season with salt to taste. Ladle the soup into individual serving bowls and garnish with a dollop of yogurt and a sprinkling of the chives.
nutrition information (per serving):
based on ten servings, Calories
4, Fat Calories
35, Saturated Fat
8, Monounsaturated Fat
20, Polyunsaturated Fat
Photo: Scott Phillips