Place chicken, broth, onion half and 2 garlic cloves in a large pot. Bring to a gentle simmer, partly cover and cook about 35–45 minutes, until every piece reaches at least 165°F in its thickest part away from bone. Transfer chicken to a clean plate. Strain and reserve the broth.

While the chicken cooks, briefly toast the stemmed and seeded chiles in a dry skillet over medium-low heat, a few seconds per side until fragrant, without blackening. Cover with hot water and soak 15 minutes, then drain.

Toast the sesame in the dry skillet until lightly golden and transfer to a bowl, reserving 1 teaspoon for garnish. Add 1 tablespoon oil and toast the almonds and tortilla pieces for about 2 minutes. Add raisins briefly until plump, then transfer everything to the bowl. Add another tablespoon oil and cook chopped onion, tomatoes and remaining garlic for 8–10 minutes until softened.

Blend the softened chiles, toasted ingredients, cooked vegetables, cinnamon, cloves and pepper with 3 cups reserved broth until very smooth. Work in batches and let hot ingredients cool enough for your blender; vent as directed by the manufacturer. Strain if the sauce remains coarse.

Heat the remaining tablespoon oil in a deep skillet or Dutch oven over medium-low heat. Carefully add the puree and stir frequently for 10 minutes. Add the chocolate and about 1 cup more reserved broth. Simmer gently for 20–25 minutes, stirring along the bottom. Add broth gradually until the sauce coats a spoon but pours easily.

Taste before adding salt. Add the cooked chicken and simmer gently for 5–10 minutes, until the chicken is hot throughout. Divide between six plates, spoon sauce over each piece and sprinkle with the reserved sesame. Rice and tortillas are optional accompaniments, not included in the recipe nutrition.