Heat a large pan to medium heat and dry-toast the ancho, guajillo, and optional chiles de árbol for 1-2 minutes per side, until the skins darken slightly. Remove from heat and place them in a large bowl. Cover the chilies with hot water and let them steep for 20 minutes, or until softened.

In the same pan, heat olive oil over medium heat. Add the chopped onion and tomatoes, cooking for 5 minutes until softened. Add the garlic and cook for 1 more minute, stirring frequently.

Transfer the cooked onion, tomatoes, and garlic to a food processor. Add the softened chilies (reserve their soaking liquid), the seasonings (oregano, salt, cinnamon, cumin, ginger, and black pepper), apple cider vinegar, and 1 cup of beef stock. Blend until smooth. For a smoother sauce, strain it through a fine sieve to remove any remaining bits.

Cut the lamb (or beef) into large chunks and place them in a large bowl. Pour the prepared birria sauce over the meat, rubbing it in to coat evenly. Cover and marinate in the refrigerator for at least 2 hours, preferably overnight for better flavor.

Add the marinated meat, including all of the sauce, to a large pot. Add the roasted tomatoes and the remaining 3 cups of beef stock. Cover the pot and cook over medium heat for 3 hours, or until the meat is fork-tender and easy to shred. If needed, add more beef stock or some of the reserved chili soaking liquid to achieve a soupier consistency.

For soup: Serve the braised birria in bowls with the rich consomé (broth).

For tacos: Shred the meat and serve on warm tortillas with consomé on the side for dipping.