Make the adobo sauce:
Heat a flat griddle or large, heavy skillet and toast the unpeeled garlic cloves, turning once or twice until they are slightly softened (they'll give slightly when squeezed) and browned in patches, about 8 minutes total. Peel.
Meanwhile, in the same griddle or skillet, toast the chiles in batches,
turning and pressing with tongs until they are fragrant, pliable, and
have turned a brighter red, about 1 minute. Transfer the chiles to a
bowl of cold water and let them soak to soften, about 20 minutes. Drain.
Toast the cumin, peppercorns, and clove in a small skillet over medium heat, stirring, until fragrant, about 1 minute.
Put
the spices, drained chiles, toasted garlic and raw garlic clove,
vinegar, oregano, salt, sugar, and 1/2 cup water in a blender and blend
until smooth, about 2 minutes, adding more water, 1 Tbs. at a time, only
if necessary to help the mixture blend properly.
Make the chile con carne and tacos
Season the beef with the salt. Heat the oil in a 5- to 6-quart heavy pot over medium-high heat and brown the meat in batches, without crowding, turning occasionally, 6 to 8 minutes per batch; transfer the meat to a bowl as it is browned.
Sauté the onion in the fat remaining in the pot (or add an extra Tbs.) over medium heat until softened, about 3 minutes.
Add the adobo sauce and cook, stirring, for 5 minutes to thicken slightly. Stir in the tomato sauce, beer, pickled jalapeños and juice, and 1 cup water and bring to a boil. Return the beef to the pot and simmer, covered, until tender, 1-1⁄2 to 2 hours.
Stir in the chocolate until melted and season with salt to taste. If necessary, simmer uncovered until the sauce is just thick enough to coat the meat.
Make tacos with the warm tortillas and the chile con carne, topping them with chopped white onion, avocado (if using), and cilantro.
