Start by soaking the prunes and raisins in lukewarm water to soften them.
In a bowl, cream the butter with the sugar until soft and fluffy.
Add the egg yolks one at a time, continuing to mix well after each addition.
Gradually fold in the sifted wholemeal flour and baking powder, stirring gently to keep the mixture soft.
Whisk the egg whites until stiff peaks form and fold them into the mixture, stirring from bottom to top to avoid deflating them.
Pour the mixture into a pre-greased or parchment-lined cake tin.
Drain the prunes and raisins from the water and distribute them on the surface of the mixture.
Peel the apples, slice them thinly, and arrange them on top of the mixture along with the prunes and raisins.
Bake the cake in a preheated oven at 180°C for about an hour or until golden and well cooked in the center.
Remove the rustic cake from the oven, let it cool slightly, and dust it with icing sugar before serving.
Notes
For an original twist, add a pinch of cinnamon or vanilla to the batter to enhance the flavor of the rustic cake with warm and enveloping aromatic notes.