Mix all the ingredients – except the milk chocolate – 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 4 mugs. Top each mug with the remaining milk chocolate.
Select ‘Air Fry’, set the time to 5 minutes and the temperature to 166°C. 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!