In a large stockpot, bring salted water to a boil. Add the remaining onion and garlic. When the water is at a fast boil, it is time to add the chicken pieces. Reduce the heat to medium and let the chicken cook until done, about 25 minutes (it will be floating on top). Check for doneness, remove and reserve. Strain the broth and reserve for the mole.
On a comal (flat griddle) or griddle set over medium-high heat, dry-roast the tomatoes, 2 onion halves and 8 cloves unpeeled garlic, about 15 minutes. The garlic will be ready sooner-when it shows brown spots, remove.
Remove the stems, seeds and veins from the chiles. Dry-roast the chiles on a dry comal. Transfer to soak in hot water, no more than 15 minutes. Heat 1 1/2 tablespoons oil in a skillet and saute the pecans and peanuts. When golden, add the sesame seeds, canela, peppercorns, cloves and oregano. Remove from the heat.
Transfer the chiles into the blender and add enough water to blend. Process until smooth, strain and reserve.
Heat the remaining 1 1/2 tablespoons oil in a large cazuela (Dutch oven) set over medium-low heat and pour the chile puree over the oil. Fry for 5 to 10 minutes. Blend the roasted tomatoes, onions and garlic and pass through a sieve. Stir into the chile paste and let the mole simmer until thickened and reduced by 3/4. Add the chocolate, 1 1/2 cups reserved chicken broth, and salt and sugar, to taste. (This will be determined by the taste of the cook, the ripeness of the tomatoes and the brand of chocolate used.) Let the sauce simmer, stirring occasionally, until the mole covers the back of a spoon.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.