Grease and line the base and both sides of each tin, then line the base with baking paper.
Add ALL the sponge ingredients to a large mixing bowl, and mix together with an electric hand mixer. Do not over mix! Continue just until the ingredients are blended together.
Preheat your air fryer to 150ºC (302ºF) for 2-3 minutes.
Divide the batter between the two tins, and place into your air fryer drawers.
Air fry on the bake setting for 13-16 minutes until a skewer inserted into the middle comes out clean.
When cool enough to handle, remove the cakes from the tins and peel away the baking paper. Place on a wire rack to cool completely.
Starting on a slow speed, beat together the butter and icing sugar in a mixing bowl with an electric hand whisk. Then increase the speed and mix until smooth, light and pale in colour.
Then add in the melted dark chocolate, and mix again until smooth and fully incorporated.
Place a sponge layer on a serving plate or cake stand, and smooth just under half the frosting over the top.
Then gently press on the other sponge layer, and smooth over the remaining chocolate frosting.
