Extract the espresso.
Whip together the egg yolks and sugar until foamy.
Add mascarpone cheese and mix well.
Beat the egg whites until stiff peaks form (make a meringue).
Fold the meringue into the yolk mixture.
Soak whole wheat castella cake in the espresso.
Layer soaked cake and cheese cream alternately in a container.
Dust cocoa powder on top to finish.
Let it chill in the refrigerator for at least 2 hours.