Preheat oven to 180 degrees Celsius, line a pan with baking paper.

Melt butter in saucepan, remove from heat and stir in sugar. Whisk in eggs one at a time and stir mixture until thick and glossy.

Sift in flour, add cocoa powder and vanilla essence with egg mixture. Stir until combined then pour into pan.

Bake for 30 min, put skewer in the middle. If it comes out clean they're ready! Cut into pieces and dust with icing sugar for appearance.