In a Dutch oven, sear the beef hunks in bacon grease. Degrease the pan. Return the beef to the pot. Stir in the flour, ground chiles, cumin and Mexican oregano. Throw in the onions, garlic and tomato purée. Add enough water to barely cover the mixture. Season to taste with salt and pepper. Stir the pot until the ingredients are well-incorporated. Bring the liquids to a rapid boil, cover the pan, cut the heat to a slow simmer and braise for 2 hours. Stir the pot - on occasion. Shred the beef hunks with two forks. Stir. Cover the pot for 10 minutes.
Place large heaps of the chili mixture into pre-warmed tortillas - along with an amount of grated cheese and/or refried beans to your liking. Fold the tortillas up burrito-style. Serve with salsa and hot sauce.