1) In a large Dutch oven, melt butter over medium heat. Add onion, and pepper; cook for 5 minutes, stirring frequently, or until tender. Add cocoa, cumin, coriander, red pepper, chicken broth, diced tomatoes, and corn. Bring to a boil over medium-high heat; cover, reduce heat and simmer for 30 minutes.
2) Puree the soup using an emersion blender or hand-held mixer. Add the tortilla chips and add shrimp. Place the pan on low heat, cover, and simmer the soup about 5 to 10 minutes or until the shrimp are just cooked.
3) Ladle the soup into serving bowls and top with a dollop of sour cream.