Prepare all the ingredients.
Melt the butter. Butter and flour a baking pan.
Whisk the eggs and sugar in a metal bowl over a bain-marie, until the temperature of the mix reaches about 40°C.
Keep whisking until fully cooled.
Combine gently with the sifted flour and cocoa, using a wooden spoon or a skimmer, stirring in a circular pattern.
This gives you a chocolated .
Pour in a buttered baking pan.
Bake in a warm oven at 180°C (356°F) for 20 to 25 minutes.
Check if the cake is bake using the blade of a knife. If it comes out dry, it is ready. Take out of the oven, unmold on a rack and leave to cool.