Place the dried chiles in a bowl and pour hot water over them. Cover and let them soak for 15–20 minutes, until softened.
Drain the chiles (reserve the soaking liquid if needed). Add chiles, garlic, onion, cumin, oregano, salt, pepper, and beef broth to a blender. Blend until smooth. Strain the sauce through a fine-mesh sieve to remove any bits of skin or seeds.
Season beef cubes with salt and pepper. Heat oil in a large Dutch oven or heavy pot over medium-high heat. Brown the beef in batches to get a nice sear. Remove and set aside.
Return the beef to the pot. Pour in the chile sauce and add more beef broth if needed to cover the meat. Stir in flour if using for thickening. Bring to a simmer, cover, and cook on low heat for 1½ hours, or until the beef is tender.
Serve hot with rice, beans, or warm flour tortillas. Garnish with chopped cilantro or onion if desired.