Beat the butter and sugar together with electric beaters until light and fluffy, around 5 mins. Whisk in the egg and vanilla extract until smooth and creamy.

Add the flour, bicarbonate of soda, chopped chocolate and a pinch of salt and mix with a spatula to form a stiff dough. Roll into 16 walnut-sized balls, then pat each one down to flatten slightly. Will keep frozen for up to three months.

Heat the air fryer at 160C and lay a piece of baking parchment in the basket. Air-fry the cookies, in batches, for 9-15 mins, until golden brown. Or air-fry from frozen for 13-15 mins. Depending on your air fryer and how you like your cookie, check every 2 mins. Leave for 2 mins to firm up then transfer to a wire rack to cool completely. Will keep in an airtight tin for up to a week.