Preheat the oven to 170°C.
Grease a 20cm non-stick cake tin with olive oil spray.
Whisk egg whites with a pinch of salt until stiff peaks form and set aside.
Whisk whole eggs, vanilla, and caster sugar until pale and doubled in volume.
Fold in the grated apple, flour, and cocoa powder using a metal spoon.
Fold a third of the whites into the cocoa mixture, then fold into remaining whites.
Spoon the mixture into the tin and bake for 30 minutes until risen.
Transfer the cake to a wire rack to cool completely.
Slice the cooled cake in half horizontally to create two layers.
Mash 100g of raspberries with 15g of icing sugar and spread over one cake layer.
Place the second cake layer on top of the fruit filling.
Mix remaining icing sugar with water to create a thin drizzle consistency.
Drizzle icing over the cake and decorate with the remaining 50g of raspberries.