Melt dark chocolate and butter together using a double boiler.
Combine eggs and erythritol in a bowl and mix well.
Add the melted chocolate into the egg mixture and blend thoroughly.
Sift almond flour and baking powder, then add to the batter and mix.
Pour the batter into a baking pan lined with parchment paper.
Bake in a preheated oven at 180°C for 20 minutes.