Simmer seasoned chicken in water or broth over medium low heat about 300°F for 25 to 30 minutes. Remove chicken and reserve 2 cups broth.
Toast dried chiles briefly, then soak in hot water for 15 minutes until soft.
Sauté onion and garlic in oil over medium heat until soft and lightly golden.
Toast sesame seeds, nuts, tortilla pieces, and bread until lightly browned.
Blend chiles, onion mixture, toasted ingredients, spices, and broth until smooth.
Simmer the sauce over low heat about 275°F for 30 to 40 minutes, stirring often.
Stir in chocolate until melted and smooth.
Add chicken back to the sauce and simmer 20 to 30 minutes.
Serve hot with sauce over the chicken.