Place your cast iron skillet over medium-high heat until it begins to smoke faintly. Add the ground beef to the dry pan, breaking it apart slightly. Let it sear untouched for 3 minutes to trigger the Maillard reaction and build a deep, flavorful brown crust before flipping.

Break the meat down into fine crumbles using your spatula. Once the pink color is 90% gone, drain any excessive pooling grease, but leave about 2 tablespoons of rendered fat in the pan for structural mouthfeel. Sprinkle the taco seasoning and kosher salt evenly over the meat, stirring constantly for 60 seconds to bloom the spices in the hot fat.

Pour the beef broth directly into the sizzling skillet, scraping up any browned bits stuck to the bottom of the pan. Reduce the heat to low and let it simmer for 4 to 5 minutes. The starches and collagen will emulsify with the fat, coating the meat in a rich, glossy sauce that prevents it from drying out on the taco bar.

Heat a separate dry griddle or skillet over high heat. Dip each corn tortilla quickly in a bowl of water (or brush lightly with oil) and place it on the hot surface for 30 seconds per side. The intense heat traps steam inside, altering the starch structure to make the tortillas incredibly pliable and strong enough to hold heavy fillings without cracking. Store them immediately in a covered tortilla warmer.

Layer each warm tortilla with 2 tablespoons of the seasoned beef base. Top with shredded lettuce, diced tomatoes, minced white onions, and a generous dusting of cotija cheese. Finish with fresh cilantro and a direct squeeze of fresh lime juice to break through the richness of the fat.