Preheat the oven to 180C. Grease the tin with the extra butter. Now break up the dark chocolate into the heatproof bowl and add the butter. Melt in the microwave on a medium setting for two minutes or until nearly melted. Stir and it will melt completely.
Put the remaining dry ingredients into the large mixing bowl. While the chocolate and butter are in the microwave, beat the eggs. Put the chocolate mixture and eggs into the dry bowl and combine.
Spread into the tin and bake for 30mins or until a knife comes out clean. Wait until cool then cut into 16 pieces. Serve with ice cream and raspberry coulis or just on it's own.