To prepare the chimichurri oil, combine all ingredients in a medium bowl, mix well, cover and set aside to infuse while the roast cooks.
Trim the fat cap of the rump roast if needed, leaving about 5mm intact. Lightly score it in a criss-cross pattern.
Rub the roast generously with olive oil, sea salt and cracked black pepper. Allow it to rest at room temperature for 30–40 minutes before cooking.
Preheat the air fryer to 200°C.
Place the beef fat-side down in the basket and cook for 10 minutes to render and crisp the fat.
Flip the roast so the fat side is facing up, reduce the temperature to 180°C and continue cooking for 35–45 minutes, depending on thickness.
For rare roast beef, remove the meat when the internal temperature reaches 50–52°C.
For medium rare, remove it at 55°C.
Transfer the roast to a plate, loosely cover with foil and rest for 15–20 minutes to allow the juices to settle.
Slice thinly and serve with the homemade chimichurri oil spooned over the top.

• Perfect served over crusty baguette with feta or ricotta.

• Always rest the meat before slicing to keep it tender and juicy.

• The chimichurri oil keeps well in a sealed jar in the fridge for up to one week.