Prepare the Filling: Heat the olive oil in a large frying pan over a medium-high heat. Add the diced onion and cook, stirring occasionally, until it becomes soft and translucent, about 5 minutes. You should hear a gentle sizzle and see the onion turning a pale golden colour. Add the minced garlic and cook for a further minute, until its sharp, pungent aroma mellows and fills the kitchen.

Brown the Meat: Increase the heat to high and add the minced beef. Break it up with a wooden spoon, letting it sear without stirring too often. You want to hear a vigorous, satisfying sizzle. Cook until the meat is deeply browned, with crispy, caramelised edges. This will take about 6–8 minutes. The sound will change from a wet splatter to a drier, sharper crackle as the moisture evaporates.

Spice and Simmer: Sprinkle the cumin, smoked paprika, oregano, and cayenne pepper (if using) over the browned meat. Stir for 30 seconds until the spices are well-coated and release their fragrance. Pour in the chopped tomatoes and tomato purée, then add the beef stock. Stir everything together, scraping up any browned bits from the bottom of the pan. Bring to a simmer, then reduce the heat to low. The mixture should be bubbling gently, not furiously. Let it cook uncovered for 15 minutes, until the sauce has thickened and the meat looks rich and glossy, clinging to the spoon.

Prepare the Taco Shells: While the filling simmers, prepare your taco shells. If using soft tortillas, pour enough sunflower oil into a small frying pan to come 1cm up the sides. Heat the oil until a small piece of bread sizzles immediately when dropped in. Carefully hold a tortilla with tongs and fold it in half, lowering one half into the hot oil. Fry for 30 seconds on each side, until it is a deep, golden brown and feels rigid. The sound of the bubbling oil is a clear sign of success. Drain on kitchen paper and gently open the shell to create a pocket. Repeat for the remaining tortillas.

Fill and Melt the Cheese: Preheat your grill to a high setting. Place the crispy taco shells on a baking tray. Spoon the hot, thick meat filling into each shell, packing it in gently. Top generously with the grated cheddar cheese. Place the tray under the hot grill for 1–2 minutes, watching closely. The cheese should bubble and turn a spotty, golden brown, and you will hear a soft, bubbling hiss as it melts over the filling.

Add the Fresh Toppings and Serve: Remove the tacos from the grill. Immediately add your chosen fresh toppings: a spoonful of soured cream, a scattering of shredded lettuce, diced tomatoes, and a few slices of pickled jalapeño. The contrast between the hot, cheesy taco and the cool, crisp toppings is the final key to the restaurant-quality experience. Serve at once, while the shells are still audibly crisp.