Preheat oven to 180 degrees C. Line one square baking pan with foil and spray with cooking spray.
In a saucepan over medium heat melt the butter. Stir in the sugar until dissolved. Remove mixture from heat, let cool and beat in the eggs one at a time mixing well after each addition. Stir in the vanilla.
Sift the flour, cocoa and salt together. Add the flour mixture to the butter mixture, mixing until combined. Stir in the walnuts. Spread the batter into the prepared pan.
Bake for 45 to 50 minutes. Do not overbake! These brownies freeze well so that you can enjoy them later.