Mix plain flour, sugar, cocoa, milk, olive oil and vanilla extract in a bowl until the mixture is thick and creamy. Add a dash more milk if the consistency is too thick and sticky.
Place 1 tbsp of the milk chocolate into each mug, then add the cake mixture on top, splitting evenly amongst the mugs. Top each mug with the remaining milk chocolate.
Select ‘Air Fry’, set the time to 5 Minutes and the temperature to 166°C / 330°F. Press ‘Start’.
When prompted to ‘Add Food’, place the 4 mugs inside the air fryer – ignore when the display indicates to ‘Turn’.
When the cooking program finishes, carefully remove the mugs and leave to cool slightly before topping with whipped cream, any remaining chocolate and a dusting of cocoa powder straight into each mug.
Enjoy immediately for delicious gooey chocolateness!