Preheat oven to 350. Grease 9x13 baking pan or line with parchment paper.
Melt Butter in medium saucepan over low heat. Remove from heat and let cool.
In a large bowl combine brown and granulated sugar.
Add melted butter to the sugars and mix well.
Add eggs one at a time. Beating well after each addition.
Stir in Vanilla Extract.
In separate bowl. Sift together Flour, Cocoa Powder, and Salt.
Gradually add dry ingredients to wet ingredients. Mixing until just combined.
Fold in chocolate chips/chunks if using.
Bake for 20-30 minutes. Until toothpick comes out with a few moist crumbs