Sauté the Aromatics: Heat the olive oil in a large, heavy-bottomed frying pan or skillet over a medium heat. Add the finely chopped onion and cook for 5-7 minutes, stirring occasionally, until it has softened and turned translucent. Add the minced garlic and cook for another minute until fragrant, being careful not to let it burn.

Brown the Beef: Turn the heat up to medium-high, add the beef mince to the pan, and break it up with a wooden spoon. Cook for 6-8 minutes, stirring and breaking it apart, until it is browned all over. I find that using the edge of the spoon to chop it into small pieces works best. Don't worry about a little moisture in the pan at this stage.

Toast the Spices: Once the beef is browned, drain off any excess fat if necessary. Sprinkle over the chilli powder, cumin, smoked paprika, oregano, salt, and pepper. Stir continuously for about 60 seconds. This step toasts the spices, which deepens their flavour immensely.

Create the Sauce: Sprinkle the plain flour over the meat and spice mixture and stir for another minute. This will help to thicken the sauce. Pour in the beef stock, then add the tomato purée and the optional brown sugar. Stir everything together until well combined.

Simmer to Perfection: Bring the mixture to a gentle bubble, then reduce the heat to low. Let it simmer for 8-10 minutes, uncovered, stirring occasionally. The sauce will thicken and reduce, coating the beef beautifully. The mixture should be moist but not watery.

Prepare and Serve: While the filling is simmering, warm your taco shells according to the package instructions. I usually place them on a baking tray in the oven at 180°C (160°C fan) for a few minutes. To serve, spoon the hot beef filling into the warm shells, then top with shredded lettuce, diced tomatoes, grated cheese, and a dollop of soured cream.