Heat a dry skillet over medium heat. Add guajillo and ancho chiles, pressing with tongs. Toast each side 2-3 minutes until fragrant and slightly darkened but not blackened. Remove stems and seeds, then soak chiles in hot water for 20 minutes until softened.
6 pieces dried guajillo chiles, 3 pieces dried ancho chiles
Drain soaked chiles and add to a blender with garlic cloves, quartered onion, cumin, vinegar, and 1 cup beef broth. Blend on high for 60-90 seconds until completely smooth with no chile skin chunks.
6 pieces dried guajillo chiles, 3 pieces dried ancho chiles, 1 white onion, 6 cloves garlic, 2 tsp cumin, 2 tbsp vinegar, 3 cups beef broth
Pat the chuck roast dry and season with salt and black pepper. Heat 1 tablespoon oil in a large skillet over high heat. Sear beef 3-4 minutes per side until a dark brown crust forms. Transfer seared beef to the slow cooker.
3 lb beef chuck roast, 1 tbsp oil, salt, black pepper
Pour the blended chile sauce over the beef in the slow cooker. Add remaining 2 cups beef broth, cinnamon stick, and bay leaves. Cover and cook on low for 8 hours. Check at 7 hours and continue if meat isn’t shredding easily.
3 cups beef broth, 1 stick cinnamon stick, 2 pieces bay leaves
Remove beef from slow cooker and rest 10 minutes. Shred with two forks, discarding large fat pieces. Skim fat from the surface of the sauce. Return shredded meat to the sauce, stir to coat, and serve in warmed corn tortillas with consommé for dipping.
3 lb beef chuck roast
