This barbacoa is slow-cooked in banana leaves for that authentic taste and that rich, complex aroma. And remember, the proper garnish, a warm tortilla and a smooth Modelo Negra can make all the difference in this delightful dish.
If using a banana leaf, run it briefly over an open flame to soften it, about 30 seconds total. Cut into 3 pieces.
Heat oven to 325 degrees. Heat the oil in a Dutch oven over medium-high. Pat the beef dry with a paper towel, sprinkle generously with salt, and lay it in the pot in uncrowded layers to brown, about 2 minutes per side. As you finish browning batches, transfer beef to a plate.
Put chiles, garlic, vinegar, sugar, oregano, and cinnamon into a blender. Add 1 teaspoon of salt and 2 cups water. Blend to a smooth puree.
When beef is browned, return it to the pot along with any liquid that may have accumulated on the plate. Pour chile puree through a medium-mesh strainer into the pot. Stir in 1 cup water. If using, nestle the pieces of banana leaf under and around the meat.
Heat sauce to a boil, then cover the pot. Bake in the oven, checking occasionally to be sure sauce comes halfway up the meat at all times (add ½ cup water if necessary) until meat is fork-tender, about 2 hours.
Use a slotted spoon to transfer meat to a platter. Heat the pan juices to a boil over medium heat and cook it until reduced enough to lightly coat a spoon. Skim any fat from the sauce and season it with salt.
When you are ready to serve, coarsely shred the beef with 2 forks and pour the pan juices over all. Serve the barbacoa with warm tortillas and garnish with onion and cilantro.