1. Preheat your oven to 350°F (175°C).
2. In a large pot, heat the vegetable oil over medium heat. Add the beef and brown on all sides.
3. Remove the beef and set aside. In the same pot, add the onion and garlic, cooking until softened.
4. Add the guajillo and ancho chiles to the pot, toasting them lightly.
5. Add the beef broth, oregano, cumin, black pepper, and apple cider vinegar. Bring to a boil.
6. Transfer the mixture to a blender and blend until smooth.
7. Return the beef to the pot and pour the blended sauce over it. Cover and cook in the oven for about 3 hours, or until the beef is tender and shreds easily.
8. Season with salt to taste and serve.