First start by preheating the oven to 350F then lightly grease an 8X8 baking pan and line it with parchment paper. Set aside.
In a medium bowl, whisk the melted butter, the brown sugar, and the granulated sugar together for about 1 minute. Add the eggs and the vanilla and beat until the colors becomes lighter. (about another minutes or two)
Sift in the flour, cocoa powder and salt and gently fold the dry ingredients into the wet ingredients just until combined. DO NO OVER MIX. Add in the nuts if you decide to use those and fold lightly.
Pour the cocoa powder brownie batter in the prepared baking pan and spread evenly then place in the oven to bake for 18-20 minutes. The brownies should be set and if tested with a toothpick should have some moist crumbs attached to it. Let the brownies cool completely before slicing into them.
If not eating these chewy brownies on the same day wrap tightly with plastic wrap and store at room temperature for up to three days or in the fridge for up to 7 days.