Creamy Carrot Soup

In 6-quart saucepot, heat oil on medium until hot. Add shallot and cook 2 to 5 minutes or until golden and tender, stirring occasionally. Add carrots, potatoes, coriander, and 1/8 teaspoon salt. Cook 5 to 7 minutes or until fragrant and starting to soften, stirring frequently. Add stock and water. Heat to boiling on high, then reduce heat to medium-low. Cover and simmer 30 minutes or until vegetables are tender. Working in batches, carefully ladle soup mixture into blender. Cover, with center part of blender cover removed to let steam escape (drape with clean kitchen towel to avoid splatter), and puree until smooth. (Can be made to this point up to 1 day ahead. Transfer to airtight container and refrigerate.) Return soup to saucepot and rewarm on low. Stir in 3/4 teaspoon salt and 1/2 teaspoon freshly ground black pepper. Divide soup among serving bowls. Garnish with cilantro, and a dollop of sour cream if desired.