1. Preheat oven to 180C/350F.
2. In a bain-marie, melt your chocolate and butter together, stir constantly until smooth and homogeneous.
3. In a separate bowl, beat together eggs and 2 types of sugars with a hand mixer for 3-4 mins until pale and fluffy.
4. Stir in your chocolate and butter mixture until combined. Fold in your flour, cocoa, vanilla and salt until just combined.
5. Transfer to a lined baking pan and bake for 30-35mins or until tested with skewer and it is 80% dry.