Cut bell peppers in half lengthwise; discard seeds and membranes. Place pepper halves, skin sides up, on a foil-lined baking sheet; flatten with hand. Broil 15 minutes or until blackened. Place in a zip-top plastic bag; seal. Let stand 15 minutes. Peel peppers. Place bell peppers, sour cream, and next 6 ingredients (sour cream through garlic) in a food processor; process until smooth, scraping sides of bowl occasionally. Place bell pepper mixture in a small bowl. Cover and chill.
Bring 6 cups of water to a boil in a Dutch oven. Add shrimp; cook 3 minutes or until done. Drain and rinse with cold water; peel. Cover and chill shrimp. Serve shrimp with sauce.