Preheat the oven to 350°F. Grease the pan and place parchment paper inside.
Melt chocolate and butter together until smooth, then allow to cool.
Beat sugar, vanilla extract, and eggs until they are light and frothy.
For a smooth mixture, sift the flour, salt, and cocoa powder.
To make a thick batter, gradually fold the dry ingredients into the wet mixture.
For a crispy, nutty texture, evenly stir in the chopped walnuts.
Bake for 25 minutes, let cool fully, cut into squares, and serve.