Cut chiles in half lengthwise; discard seeds and membranes. Place chile halves, skin side 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.
Heat oil in a large Dutch oven over medium-high heat. Add onion to pan; saute 3 minutes. Add cumin, coriander, and garlic to pan; saute 1 minute.
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 and cool for 5 minutes.
Place half of tomato mixture in a blender. Remove center piece of blender lid to allow steam to escape, and secure lid. Place a clean towel over opening in lid to avoid splatters. Blend until almost smooth. Pour into a large bowl. Repeat with remaining tomato mixture. Stir in juice and salt.
Top servings of soup with cilantro and sour cream; serve with lime wedges if desired.