De-stem and de-seed the dried chiles, then cut into strips (scissors sometimes work better than knives for this) and place in the blender.
Heat the chicken broth, then pour into the blender as well. Let the peppers steep about 10 minutes to soften.
Blend to make sure the peppers are breaking up. Then add the tomatoes, tomatillos, onion, garlic, almonds, raisins, and chocolate. Blend to make a thick sauce, then pour into the slow cooker. Work in batches if you need to, it'll all get mixed together in the slow cooker anyway.
Stir in the pepper, cinnamon, coriander, cumin, and sugar. Salt the chicken, then add to the slow cooker. Lightly toss in the sauce to coat, then cover and cook until the chicken is tender, about 4 hours on high or 8 hours on low.
Serve topped with sesame seeds and enjoy!