Place chicken pieces in a large resealable plastic bag. Combine the tequila, lime juice, garlic, cilantro and brown sugar in a mixing bowl and whisk until the sugar is dissolved. Pour over chicken pieces and seal the bag, trying to release as much air as possible. Refrigerate the chicken for 45 minutes to 1 hour, turning occasionally.

While the chicken is marinating, make the sauce.

Preheat the broiler to 500 degrees F and line a large baking sheet with parchment paper.

Combine the tomatoes, onion, and garlic cloves on the baking sheet and broil until slightly caramelized around the edges, about 10 minutes. Remove from the oven and transfer the garlic to a small plate to cool. Using a spatula or large spoon, turn the tomatoes and onions so that the uncooked sides are up. Return to the broiler until slightly caramelized on the second side, about 6 to 8 minutes. Remove from the oven and set aside to cool. In a large skillet over high heat, toast the chiles on all sides until lightly browned and fragrant. Do not allow to burn. Transfer to a medium bowl, cover with hot water and allow to sit until softened, about 30 minutes. In the same skillet, combine the sesame seeds and reserved chile seeds and toast until light brown and fragrant. Transfer to a large bowl and set aside. Add the peppercorns, cinnamon stick, cloves, oregano and thyme to the hot skillet and "toast" for a few seconds, just until their perfume is released. Transfer to the bowl with the sesame seeds.

When cool enough to handle, peel the garlic cloves and add these, along with the charred tomatoes and onion, to the bowl of a food processor. Add the seeds and spices. Drain the liquid off of the chiles and add these to the processor as well. Add the roasted nuts and raisins, and 1 cup of the chicken stock and puree the mixture until very smooth and thick, scraping down the sides of the blender frequently.

In a large deep pot, heat 3 tablespoons of the vegetable oil until very hot. Carefully pour the pureed mixture into the pot (be careful ? it will splatter) and bring the mixture to a boil. Lower the heat so that the mixture simmers, and add 3 1/2 ounces of the chocolate to the pot. Cover and cook, stirring frequently, for about 1 hour, or until the mole paste is very thick and flavorful. At this point you should have about 3 1/2 cups of mole paste. Reserve 1 cup to make the Mole sauce, and reserve the remaining paste for another use. The mole paste will keep for at least 6 months, refrigerated, or up to 1 year if frozen.

Preheat the broiler to 500 degrees F.

To make the sauce, heat the remaining 1 1/2 tablespoons of oil in a large saucepan over medium-high heat until very hot. Add the tomato puree and cook for 2 minutes, stirring frequently. Add the cup of reserved mole paste and the remaining 1 to 1 1/2 cups of chicken stock and stir to combine well. Cook for 3 to 4 minutes, until the mixture is a nice sauce consistency. Add the remaining 1/2-ounce of Mexican chocolate and the salt and cook another 2 minutes, or until the chocolate is melted and the sauce is thick, smooth and flavorful. Keep warm while you cook the chicken.

Line a baking sheet with aluminum foil and place the chicken pieces on the baking sheet. Broil for 5 minutes, or until the chicken is charred in places. Turn the chicken and continue to broil for an additional 5 minutes, or until the second side is charred. Reduce the heat to 325 degrees F and continue to cook the chicken until the juices run clear, about 10 more minutes.

Serve the chicken immediately, with some of the mole sauce spooned over the top, garnished with some of the chopped cilantro. Pass tortillas at the table.