Preheat and prepare the pan

• Preheat the oven to 350 °F.
• Spray a 9x13 pan with cooking spray and set aside.

Beat the butter and sugar

• Place the room-temperature salted butter and the sugar in a stand mixer fitted with the paddle attachment.
• Beat until light and fluffy and no longer yellow, scraping down the sides as needed.

Add the eggs and vanilla

• Add the eggs one at a time on low speed, mixing well after each addition.
• Add the vanilla extract and mix to combine.

Whisk the dry ingredients

• In a separate bowl, whisk together the flour and cocoa powder until there are no lumps.

Combine the batter

• Slowly add the flour mixture to the wet ingredients, mixing just until combined.
• Scrape down the sides and avoid overmixing.
• Fold in the chocolate chips or nuts.

Bake the brownies

• Spread the batter evenly into the prepared pan.
• Bake until set in the center.

Cool and serve

• Let the brownies cool in the pan before cutting into squares.