Prepare the dried chiles. Remove stems and seeds. Toast them lightly in a dry skillet over medium heat (about 30 seconds per side) until fragrant. Be careful not to burn them.
Rehydrate. Place the toasted chiles in a bowl and cover with hot water. Let them soak for 20 minutes until softened.
Blend the sauce. In a blender, combine the softened chiles, garlic, onion, cumin, oregano, and 2 cups beef stock. Blend until smooth. Strain through a fine-mesh sieve for a silky texture.
Sear the beef. In a heavy-bottomed pot or Dutch oven, heat oil over medium-high heat. Season the beef with salt and pepper, then brown in batches until golden on all sides. Remove and set aside.
Simmer. Return beef to the pot. Pour in the red chile sauce and remaining beef stock. Bring to a boil, then reduce heat to low, cover, and simmer for 1 ½ to 2 hours, stirring occasionally, until the beef is tender and the sauce has thickened.
Taste and adjust. Add salt as needed. If sauce is too thick, stir in a little more stock or water.
Serve. Ladle chile colorado into bowls with rice or scoop it into tortillas. Garnish with cilantro or onions.