Preheat oven to 170C

Grease 20cm cake tin with a few sprays with the cooking spray.

In a stand mixer, whisk the 4 egg whites and salt to peaks.

In a large bowl, hand whisk the 2 whole eggs, vanilla extract and caster sugar together until combined and the sugar has dissolved.

With a plastic spatula gradually fold the apple, self-raising flour and cocoa powder into the sugar mixture.

Gradually fold the egg white peaks into the sugar mixture, keeping the mixture as light and fluffy as possible.

Carefully spoon the cake mixture into the greased cake tin.

Bake for 30 – 40 minutes. Test the cake after 30 minutes with a skewer. If the skewer comes out clean then the cake is cooked.

Cool on a wire rack.

Once cooled, remove the cake from the cake tin and cut it in half horizontally.

Mash 100g of the raspberries with some icing sugar to make a kind of “jam”. Spread this mixture between the cake halves.

Mix some of the icing sugar with water to make a weak icing and spread over the top of the cake.

Decorate the top of the cake with the remaining raspberries. Allow the icing to harden.