Melt the dark chocolate and butter together using a double boiler.
Mix sugar and eggs together and whisk until combined.
Add the egg mixture to the melted chocolate and mix well.
Sift in cake flour, cocoa powder, baking powder, and salt. Mix until just combined.
Let the dough rest in the refrigerator for 1 hour.
Shape the dough into balls and roll them in powdered sugar.
Bake in a preheated oven at 180°C (356°F) for 10-12 minutes.