Preheat the oven to 360F.
Divide eggs.
In a deep bowl, beat 4 egg whites on high speed using an electric mixer.
When egg whites turn nice and fluffy, put them aside for the time being.
In a separate bowl, combine flour, baking powder and cocoa.
Combine egg yolks, sugar and oil. Mix together with an electric mixer and once ingredients are well combined, reduce speed to low. Begin adding the shredded apples and flour mixture alternating between the two until fully mixed.
Add egg whites into the mixture and combine with a wooden spoon
Add raisins and walnuts if desired.
Lightly grease the bottom of a 9x13 glass plan.
Pour mixture into the pan and bake for 25 minutes.
Insert toothpick to check if the cake is fully cooked in the center. Avoid overcooking this dessert, better to be undercooked than over-cooked.
Remove from the oven and allow it to cool.
Sprinkle with powdered sugar if desired and cut into 1" squares.