Melt the dark chocolate and butter together using a double boiler.
Whisk eggs and sugar until foamy.
Mix the melted chocolate mixture into the eggs.
Sift in cake flour, baking powder, and unsweetened cocoa powder, then mix.
Pour the batter into a madeleine mold.
Bake in a preheated oven at 180°C for 10 minutes.
Let cool and finish.