Fill ¼ water on a small saucepan and put over a lower heat. Place a medium bowl on top of the saucepan without touching the water.
Put butter and dark chocolate into the bowl and stirring occasionally until butter and chocolate have melted.
Add sugar to the bowl while it’s on the saucepan and whisk well.
Remove the bowl from the pan and add eggs one by one while whisking.
Add coffee, salt, vanilla, dark chocolate powder and flour, Mix all together.
Pour the mix into a baking tray and bake for 30 minutes at 180 °C (350 °F)