3dried ancho chilies, seeded, stemmed, and torn into pieces
2dried chipotle chilies, seeded, stemmed, and torn into pieces
3 clovesgarlic, peeled and smashed
2 cupschicken broth, divided
1 tbspdried oregano
1 tbspground cumin
1 tspground coriander
2 tbspvegetable oil
1white onion, sliced
Set a saute pan over medium heat and add the chilies and garlic. Toast until fragrant, about 5 minutes. Add 1½ cups broth to the pan and turn off the heat. Let the chilies soak and the broth cool for 10 minutes. Transfer to the bowl of a blender along with the oregano, cumin, coriander, and salt. Puree.
Return the pan to the stove, add 2 tbsps of vegetable oil, and set over medium-high heat. Once the oil is shimmering, place the chuck roast in the pan and sear for 1 minute on each side. Remove from pan and place in the crock of a slow cooker.
Add the sliced onion to the hot pan and saute until golden, 8-10 minutes. Add the extra½ cup of chicken broth to the pan and use a wooden spoon to scrape up any brown bits stuck to the bottom. Transfer the onions to the slow cooker.
Pour the pureed chili pepper mixture on top of the beef and onions. Set the slow cooker to low and cook for 8-10 hours, until fork tender.
Remove the beef from the cooker and shred with a fork. Skim the fat from the liquid in the slow cooker and toss the juices with the shredded meat.