In a large pot, combine chicken, whole onion, 3 garlic cloves, salt, and 8 cups water

Bring to a boil, then reduce to medium-low, cover, and simmer for 15 minutes

Cook until chicken reaches 165°F internally

Remove chicken and set aside

Strain and reserve broth for mole sauce

Preheat oven to 475°F

Place guajillo, ancho, and pasilla chilies on a foil-lined baking sheet

Toast in the oven for 6 minutes, flipping halfway through

Transfer to a large bowl and soak in warm water for 30 minutes to 1 hour

Drain and set aside

On the same sheet pan, roast the quartered tomatoes and sliced onion for 20 minutes

Look for deep browning or light charring on the bottom—this adds depth

In a blender, combine roasted tomatoes, onion, garlic cloves, prunes, toasted tortillas, salt, cinnamon, oregano, cloves, and 3 cups chicken broth

Blend until smooth (about 3 minutes)

Heat 2 tbsp olive oil in a large pot over low heat

Strain blended sauce through a fine mesh strainer into the pot

Reserve about 1 cup of this sauce in the blender

Add the soaked chilies and 3 more cups of broth to the blender with the reserved sauce

Blend until completely smooth (3–4 minutes)

Strain into the pot and stir to combine with the first sauce layer

Bring sauce to a simmer over medium heat

Once bubbling, reduce to medium-low, cover, and simmer for 30–45 minutes

The longer it simmers, the thicker and richer the sauce becomes

Stir in chocolate, peanut butter, and sugar until melted and smooth

Simmer for another 5 minutes

Taste and adjust salt, sweetness, or spice as needed

Arrange chicken pieces in a large shallow bowl or deep platter

Generously ladle the mole sauce over the chicken

Serve hot with fluffy Mexican rice, warm tortillas, and garnishes like fresh cilantro and toasted sesame seeds