Sauté the Aromatics: Heat the oil in a large, heavy-based frying pan or skillet over a medium heat. Add the finely chopped onion and cook for 5-7 minutes, stirring occasionally, until it's soft and translucent. Add the minced garlic and cook for another minute until fragrant.

Brown the Beef: Turn the heat up to medium-high. Add the beef mince to the pan. Use a wooden spoon or a spatula to break it up. I find that a potato masher works wonders for getting a fine, even texture. Cook for 5-8 minutes, until the beef is nicely browned all over. A good browning is crucial for flavour, a process known as the Maillard reaction. Drain off any excess fat if necessary.

Bloom the Spices: Reduce the heat to medium. Add the chipotle paste, ground cumin, smoked paprika, and dried oregano to the pan with the beef. Stir everything together constantly for about 1 minute. This step, known as blooming, toasts the spices and deepens their flavour.

Simmer the Sauce: Pour in the chopped tomatoes and the beef stock. Add the salt and black pepper, then stir everything thoroughly to combine. Bring the mixture to a lively simmer.

Reduce and Thicken: Once simmering, reduce the heat to low, cover the pan with a lid, and let it bubble away gently for 15 minutes. After 15 minutes, remove the lid and continue to simmer for another 5 minutes, allowing the sauce to reduce and thicken until it clings beautifully to the meat.

Prepare and Serve: While the beef is simmering, warm your tortillas according to the packet instructions. Prepare all your toppings and place them in small bowls. Once the beef filling is ready, give it a final stir and taste for seasoning, adding more salt if needed. Serve immediately, letting everyone build their own spicy beef tacos.