Cooking a topside beef roasting joint in an air fryer is a brilliant way to achieve a beautifully tender and juicy roast with a delectable crispy exterior. Begin by seasoning the beef generously with salt, black pepper, and your favourite herbs, such as rosemary or thyme, to enhance the flavour. Preheat your air fryer to about 200°C (390°F) to ensure a robust sear. Place the joint in the basket, allowing space for air circulation, and roast for approximately 25-30 minutes per 500g, adjusting the time depending on your desired level of doneness. Keep an eye on the internal temperature; medium-rare should reach around 55°C (130°F), while medium will sit closer to 65°C (150°F). Once cooked to perfection, rest the beef for at least 15 minutes before slicing. This technique not only reduces cooking time but also ensures a succulent roast that's sure to impress at any Sunday dinner. Serve with golden roast potatoes and seasonal vegetables for a delightful meal.