Take the beef out of the fridge and bring it up to room temperature before cooking (20-30 mins should do it).

Heat the air fryer to 220C. Rub the beef all over with the oil, then combine the thyme, onion granules and mustard powder with 1 tsp salt and 1 tsp ground black pepper in a bowl. Rub this all over the beef joint, then put the beef in the air fryer basket and cook for 10 mins.

Reduce the temperature to 170C, then cook for a further 30-40 mins (30 mins for medium-rare and 40 mins for medium-well done). Transfer the meat to a board, cover loosely with foil, and leave to rest for up to 30 mins before carving and serving.