Grease a shallow baking tin (20cm x 18cm x 8cm – or whatever fits in your air fryer basket).

Put the butter, golden syrup, sugar and vanilla in a microwave-safe bowl.

Heat in 30-second bursts, stirring between bursts, until the butter is dissolved and you have a dark liquid.

Add the oats. Stir until they’re well coated.

Add the egg and stir through, aiming to distribute it right through the mixture.

Transfer the mixture to the greased tin and press down firmly all over.

Set the air fryer to 160C/320G and bake for 20 minutes, or until golden brown on top, then leave to cool completely.

If it seems at all crumbly, place in the fridge to firm up.

Transfer to a chopping board and cut into 16 pieces (in a 4 x 4 pattern) with a sharp knife.