Preheat the oven to 170°C (338°F).
Melt the sugar-free dark chocolate and butter together using a double boiler.
Crack the eggs into a bowl and mix with erythritol.
Combine the melted chocolate with the egg mixture, mixing well.
Add almond flour and baking powder, then mix to form a batter.
Pour the batter into a baking pan.
Bake in the oven at 170°C (338°F) for 20 minutes.
Let it cool, then cut into pieces for serving.