Preheat oven to 160ºC (fan forced). Spray a 23cm springform cake tin with non-stick spray, line with baking paper and set aside.
Place egg whites into a mixing bowl, add salt and whisk on high speed until stiff peaks form.
In another bowl, add the egg yolks and brown sugar and whisk for 2 minutes until frothy and lighter in colour. Whisk in the oil and cream then add the almond flour, coconut and cinnamon and stir until well combined.
Gently fold in the whipped egg whites a little at a time, until no lumps are visible.
Pour one third of the cake batter into the cake tin, layer with apple slices, then another third of batter, layer with apple slices and then the final layer of batter and layer with sliced apples. Sprinkle with flaked almonds and castor sugar.
Bake for 45-50 minutes then set on a cooling rack to cool completely before removing it from the tin. Dust with icing sugar (if desired) and serve.