Melt the dark chocolate and butter together in a double boiler.
Add erythritol to the melted chocolate and mix well.
Add the eggs all at once and mix thoroughly.
Sift in almond flour and cocoa powder, then gently fold to combine.
Pour the batter into a pan and smooth the surface evenly.
Bake in a preheated oven at 180°C (356°F) for 20 minutes.
Let it cool and cut into bite-sized pieces.