In a medium-size bowl add the egg yolks and half the sugar and whisk or beat until it thickens and is a light yellowish color.
In a separate large bowl mix together the flour, baking powder, vanilla extract and butter for a few seconds.
Add in the egg yolk mixture and mix until the dough comes together.
Portion the dough into three, equal parts.
Save one of the dough pieces and add the cocoa and mix until well combined.
Wrap the divided dough pieces in plastic cling wrap and place it into the refrigerator for at least 2 hours.
Preheat the oven at 350°F (175°C) with the rack in the middle position.
Add the egg whites and beat with the sugar in a medium-size until stiff peaks and set aside.
To assemble the cake: Grease a 13 x 9-inch pan with cooking spray.
Remove one of the white dough pieces and using a rolling pin, roll it out to fit the bottom of the baking pan.
Spread your filling of choice evenly throughout the top of the dough.
Take out the cocoa dough and grate it.
Place the grated cocoa dough over the top of the bottom dough with the filling.
Add the egg white mixture (meringue) onto the grated cocoa dough and spread it out evenly.
Remove the last dough piece and shred it over the top of the meringue.
Place into the preheated oven and bake for 45-60 minutes.
Remove from oven and cool.
Dust with icing sugar and serve.