Melt the dark chocolate and butter using a double boiler.
Add sugar to the melted chocolate and mix well.
Add eggs and stir to make a batter.
Sift in the flour, cocoa powder, and salt, and gently fold together.
Chop walnuts or pecans and add them to the batter.
Pour the batter into a baking pan and spread it evenly.
Bake in a 180°C (356°F) oven for 25-30 minutes.
Let cool and cut into pieces.