Preheat the oven to 180°C (356°F).
Combine eggs and sugar in a bowl and mix well.
Melt dark chocolate and butter together using the double boiler method.
Add the melted chocolate mixture to the egg batter and mix.
Sift in whole wheat flour, cocoa powder, protein powder, and baking powder, then mix until well combined.
Add milk and adjust the consistency of the batter.
Pour the batter into a mold and bake for 25–30 minutes.
Let cool, then cut into desired serving sizes.