Preheat the oven to 160°C/325°F/ Gas 3. Place the meat on a sheet of foil and rub it all over with the oil. Sprinkle both sides with the salt, oregano and cumin and rub in well. Add the onion and garlic. Top with another sheet of foil and roll up to seal the edges, leaving room for some steam expansion during cooking.

Place in a baking dish and bake for 3 hours, until the meat is tender enough to shred. Remove from the foil and shred the meat using two forks.

Stir 120 ml (4 fl oz) 1/2 cup of the enchilada sauce into the beef. Spoon a thin layer of enchilada sauce on the bottom of a rectangular baking dish, or in four individual dishes.

Place the remaining sauce in a frying pan and warm gently.

Put a 1 cm (1/2 in) layer of vegetable oil in a second frying pan and heat until hot but not smoking. With tongs, lower a tortilla into the oil; the temperature is correct if it just sizzles. Cook for 2 seconds, then turn and cook the other side for 2 seconds. Lift out, drain over the pan, and then transfer to the pan with the sauce. Dip in the sauce just to coat both sides.

Transfer the softened tortilla immediately to a plate. Spread about 2 - 3 spoonfuls of the beef mixture down the centre of the tortilla. Roll it up and place the filled tortilla seam-side down in the prepared dish. Repeat this process for all the remaining tortillas.

Spoon the remaining sauce from the frying pan over the beef enchiladas, spreading it right down to the ends. Sprinkle the grated cheese down the centre.

Bake the enchiladas until the cheese topping just melts, for about 10 - 15 minutes. Sprinkle with chopped spring onions and serve at once, with soured cream on the side.