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, add your melted butter, granulated sugar, brown sugar, and vanilla, stirring to combine. Add eggs and stir until completely incorporated.
In a separate bowl, sift together your dry ingredients - flour, cocoa, and salt. Slowly stir dry ingredients into wet ingredients until combined. Scrape down the sides of your bowl.
Stir in chocolate chips and walnuts. Pour into your prepared 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. Baking time will increase by up to 5 minutes.