Preheat oven to 180ºC (350ºF). Grease a 9" x 13" baking pan. Sprinkle a little cocoa into the pan and shake to coat surface and sides.
Put butter and sugar into a bowl and beat well until light and creamy. Beat in the eggs one at a time, until well blended. Stir in vanilla extract beating until fluffy.
Combine all dry ingredients: flour, cocoa powder, baking powder and salt in a separate bowl. Add dry ingredients to butter mixture. Blend until combined but do not over mix. Stir in chopped nuts.
Pour the mixture to the prepared pan. Bake for 30-35 minutes or until done. Cool then cut into squares and serve.
