Step 1

Bring guajillo chiles, pasilla chiles, and 2 cups water to a boil in a medium saucepan over high heat. Remove from heat, cover, and let sit until chiles are very soft and fall apart easily, about 30 minutes.

Step 2

Meanwhile, toast tortilla pieces in a medium skillet over medium high heat, tossing occasionally, until lightly charred, about 4 to 6 minutes. Transfer to a small heat-proof bowl. In the same skillet over medium-high heat, toast peppercorns, bay leaves, cloves, cinnamon, and cumin seeds, stirring constantly, until very fragrant, about 1 minute. Add the oregano, stirring constantly, until very fragrant and lightly toasted, about 30 seconds. Transfer spices to the bowl with the tortilla.

Step 3

When the chiles have softened, add them to a blender with their liquid, the toasted tortilla and spice mixture, and the garlic, chocolate, and salt. Blend mixture, starting at low speed and gradually increasing to high, until completely smooth, about 1 minute 30 seconds.

Step 4

Arrange a rack in the lower third of the oven and preheat to 500°F.

Step 5

Place the chuck roast in a large roasting pan and pour the chile puree on top. Add the orange juice to the blender, pulse a few times to clean the jar, then pour over the roast. Pour 8 cups of water around the roast and cover the pan tightly with two layers of aluminum foil, crimping around the edges to trap the steam inside. Roast for 30 minutes, then reduce the oven temperature to 250°F and continue to roast until the meat is very tender and shreds easily, 4 to 4½ hours.

Step 6

Remove the pan from the oven and set aside, still covered, for about 1 hour, or until the roast is cool enough to handle. Shred the meat into small pieces and place in a large bowl.

Step 7

Transfer the pan juices (the consommé) to a large bowl or pot. Taste and season with additional salt, if necessary.

Step 8

Divide the meat among shallow bowls and drizzle the consommé on top. (If you like, you can also pour some consommé into a small bowl for dipping.) Serve with chopped onion, cilantro, lime wedges, salsa, and tortillas for making tacos.