01 - Preheat oven to 350°F. Grease or line an 8x8-inch baking pan with parchment paper.
02 - In a bowl, whisk together all-purpose flour, unsweetened cocoa powder, and salt. Set aside.
03 - In a separate bowl, whisk the melted unsalted butter with granulated sugar and brown sugar until the mixture is smooth and glossy.
04 - Beat in the eggs one at a time, then stir in the vanilla extract until fully incorporated.
05 - Fold the dry mixture into the wet mixture until just combined. Avoid overmixing.
06 - Gently fold in chocolate chips and chopped nuts, if using.
07 - Pour batter evenly into the prepared baking pan and smooth the surface.
08 - Bake for 23 to 27 minutes, until the center is just set and a toothpick inserted in the middle comes out with moist crumbs.
09 - Let brownies cool completely in the pan before slicing into 16 squares.