Sift all purpose flour, cocoa powder and baking soda together. Add butter and sugar in a bowl and mix it together with the hand mixer.
Add all the dry ingredients to the wet ingredients. Blend it together pproperly.
Pre-heat oven to 356℉ or 180℃. Grease the pan with the cooking spray. Pour the mixture in the greased pan. Sprinkle walnuts or almonds on the brownie batter.
Bake for 25-30 minutes. Let it cool down in the pan for 10 minutes. Cool it completely on a wire rack. Cut into slices after it is completely cool down.