Stir all Spice Mix ingredients together in a bowl, then measure out 4 teaspoons and press it onto the beef pieces. The seasoning should form an even coating with no loose piles of spice falling away.

Heat the olive oil in a large heavy-based pot over high heat, then sear the beef in batches until every side is deeply browned; set the beef aside on a plate. Look for a dark mahogany crust and browned residue on the bottom of the pot.

Lower the heat to medium and add more olive oil if the pot looks dry. A light coating of oil should remain so the aromatics soften without scorching.

Add the garlic and onion and cook for 3 minutes. The onion should soften and smell sweet and savory, while the garlic stays fragrant rather than browned.

Pour in the orange juice and lime juice, scraping the bottom of the pot as the liquid bubbles. The browned bits should dissolve into the citrus instead of staying stuck to the pot.

Stir in the crushed tomatoes, broth, water, and remaining Spice Mix, then return the beef and any collected juices to the pot. The beef should sit in a well-seasoned braising liquid with the spices evenly distributed.

Cover the pot and bring the liquid to a simmer, then lower the heat until it bubbles gently. Keep the surface moving quietly, not boiling hard, so the beef fibers stay tender.

Cook covered for 2 hours, then remove the lid and continue simmering for 30 minutes. The beef is ready when a fork slides in easily and the meat pulls apart without rubbery resistance.

Lift the beef from the pot and pull it into shreds with two forks. Fork-tender meat separates into moist strands instead of resisting or breaking into dry chunks.

Simmer the sauce uncovered for 10 to 15 minutes, season with salt to taste, and optionally blend it smooth with an immersion blender. The finished sauce should lightly coat a spoon rather than run off like thin broth.

Return the shredded beef to the reduced sauce and toss until coated. Every strand should look glossy and richly seasoned.

Transfer the beef to a large dish and serve with warmed tortillas and desired taco toppings. Keep the beef warm and saucy so it stays tender from the first taco to the last.