Whisk the eggs and sugar with an electric whisk until thick and voluminous. Mix in the melted butter. Sift over the flour and cocoa powder, add the chocolate chips and mix to combine. Cover and chill for 1 hr. Dough will keep chilled in an airtight container for up to a week.

Heat the air fryer to 170C and put a square of baking parchment in the basket. Shape heaped teaspoons of the mixture into balls. If cooking straight away, roll the balls in the icing sugar until well coated. Put on the parchment, leaving plenty of room for them to spread out. The un-dusted cookie balls can be frozen for up to two months.

Air fry in batches for 8-10 mins (or 10-12 mins from frozen), then leave to cool and firm up for a few minutes before carefully transferring to a wire rack to cool completely. Will keep in a tin for five days.