1. Preheat broiler.
2. In small bowl, stir together cilantro and sour cream. Transfer to bowl and chill until ready to serve.
3. Cut bell peppers lengthwise, and place skin-side up on broiler pan. Broil 4 inches from heat until skin is blackened, about 12 minutes. When peppers are cool enough to handle, peel them with sharp knife.
4. In nonstick Dutch oven, heat oil over medium-high heat. Stir in onions, garlic, salt, and black pepper, and sauté until onions are softened slightly, about 2 minutes.
5. Add bell peppers and water to pan. Cover and bring to a boil. Reduce heat to medium-low, and cook until peppers and onions are very tender, about 10 minutes.
6. In food processor or blender, purée soup. Return purée to saucepan. Add beans, and cook over medium heat until warmed through. Serve soup topped with cilantro cream.