Preheat the oven to 170°C (338°F).
Melt dark chocolate and butter together using a double boiler.
In a large bowl, add eggs and sugar, then mix well.
Add the melted chocolate and butter mixture to the egg batter and mix.
Sift flour, cocoa powder, and baking powder into the bowl, then fold in with a spatula.
Line a baking pan with parchment paper and pour in the batter.
Bake in the preheated oven at 170°C (338°F) for 25-30 minutes.
Let cool, then cut into pieces of desired size.