Preheat your air fryer to 200 degrees Celsius (400 Fahrenheit)
Wash and dry 400 grams of small potatoes
Add the clean potatoes to the preheated air fryer and air fry for 15-20 minutes until the potatoes are soft.
Remove the cooked potatoes from the air fryer, and place them on a flat board or tray. Use a potato masher, large fork or the base of a heavy flat-bottomed glass to smash the potatoes.
Return the smashed potatoes to the air fryer, brush or drizzle the potatoes with the butter and olive oil and season with a sprinkle of salt.
Air fry the smashed potatoes for a further 25-30 minutes at 180 degrees Celsius (360 Fahrenheit). Or until crispy.