Grease an 8x8 square baking pan or line with parchment and set aside. If lining pan, leave some hanging over the edges to easily pull brownies from the pan once cooled.
In a large mixing bowl, combine melted butter, sugars, and vanilla. Beat in eggs.
In a separate bowl, sift together dry ingredients - flour, cocoa, and salt. Slowly stir dry ingredients into wet ingredients until combined.
Stir in chocolate chips and walnuts. Pour into 8x8 pan and use a spatula to spread evenly to the edges. Batter will be thick.
Bake for 20-24 minutes, then test with a toothpick for doneness. Insert toothpick into the center of the pan. If toothpick comes out with wet batter, the brownies are not done. Continue checking every 2 minutes. If toothpick comes out with a few crumbs, then the brownies are done.
Place brownies onto a wire rack and allow to cool completely before cutting and enjoying.
Brownies will keep for 4-5 days in a sealed container at room temperature.
Dutch cocoa can be substituted with natural cocoa powder.
Walnuts can be omitted or substituted with chopped pecans, almonds, or peanuts.
Doubled recipe can be prepared in a 9x13 pan (brownies will be slightly thinner), baking time may increase by up to 5 minutes.