Preheat 180°C and line a 9x5 inch loaf tin with oil and baking paper.
Melt the butter and chocolate until smooth, either in a microwave with 10-second intervals until melted through or over the stove stirring constantly. Set aside to cool.
In a large bowl whisk the eggs and sugars together until thick and a golden tan color. It should take around 3-4 minutes of whisking vigorously.
Pour the cooled, melted chocolate mixture into the egg mixture and whisk well until combined.
Switch to a spatula and fold in the dry ingredients, i.e. the flour, cocoa powder, salt and vanilla. Do not over mix the batter at this stage.
Pour the batter into the prepared tin and bang the tin against the surface to release the excess air bubbles.
Bake for 32-35 mins until the top is cracked and shiny. A toothpick inserted should come out with wet moist and sticky chocolate cake crumbs or should have a jam like cake texture.
What it shouldn’t have is raw batter as this means the brownie isn’t baked in the center yet.
Leave to cool for an hour in the tin and remove, transfer to a cooling rack and leave for another hour before cutting into squares and enjoying.