Make the Tangy Burger Sauce: In a small bowl, whisk together mayonnaise, ketchup, mustard, relish, apple cider vinegar, smoked paprika, garlic powder, onion powder, and cayenne (if using). Taste and adjust seasoning. Cover and refrigerate while preparing the rest.

Preheat a large cast-iron skillet or griddle over medium-high heat for 3–4 minutes until very hot. Lightly brush one side of each corn tortilla with melted butter. Working in batches, place tortillas butter-side down in the dry skillet and toast for 30–45 seconds per side until lightly charred and pliable. Transfer to a clean kitchen towel and cover to keep warm.

Return the skillet to high heat and add vegetable oil. Once shimmering, place 4 beef balls in the skillet, spaced apart. Immediately smash each ball flat with a sturdy metal spatula or burger press to form thin 4-inch patties, pressing firmly to create maximum surface contact. Season generously with salt, pepper, garlic powder, and onion powder.

Cook patties undisturbed for 2–3 minutes until deeply browned and crisp at the edges. Flip, season the second side, and immediately top each patty with a slice of American cheese. Cook 30–60 seconds more until cheese is melted. Repeat with remaining 4 beef balls.

To assemble: Place a warmed tortilla on a plate. Spread 1 tablespoon of Tangy Burger Sauce over the surface. Add a handful of shredded lettuce, then place one cheesy smash patty on top. Garnish with diced onions and pickle slices. Repeat for remaining tacos. Serve immediately with extra sauce on the side.

Pro tip: For extra crispiness, press the assembled taco gently in the hot skillet for 15 seconds per side before serving — this fuses the patty to the tortilla and adds a delicious crunch.