1. Preheat broiler.
2. Cut chiles in half lengthwise; discard seeds and membranes. Place chile halves, skin sides up, on a foil-lined baking sheet; flatten with hand. Broil 18 minutes or until blackened. Place in a zip-top plastic bag; seal. Let stand 10 minutes. Peel and coarsely chop.
3. Heat oil in a large Dutch oven over medium-high heat. Add onion to pan; sauté 3 minutes. Add cumin, coriander, and garlic to pan; sauté 1 minute.
4. Using kitchen shears, coarsely chop tomatoes in the can. Add tomatoes, chiles, and broth to pan, stirring to combine; bring to a boil. Reduce heat, and simmer 30 minutes. Remove from heat; cool 5 minutes.
5. Place half of tomato mixture in a blender. Remove center piece of blender lid (to allow steam to escape), and secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until almost smooth. Pour into a large bowl. Repeat procedure with remaining tomato mixture. Stir in juice and salt. Ladle about 1 cup soup into each of 6 bowls; top each serving with 1 tablespoon cilantro and 1 teaspoon sour cream. Serve with lime wedges, if desired.