Combine eggs, protein powder, and unsweetened cocoa powder in a bowl and mix well.
Add Greek yogurt and erythritol, then mix again.
Add baking powder and finish the batter.
Line a pan with parchment paper and pour in the batter, smoothing it flat.
Bake in a preheated oven at 180℃ for 20 minutes.
Let it cool completely, then cut into pieces.