Preheat oven to 350 degrees F
Line a 9x9 inch square cake pan (for thick brownies) or 9x13 inch pan (for thinner brownies)with parchment paper
Melt butter and chocolate in a microwave safe bowl, stirring every 30 seconds until melted
Whisk sugar, eggs, salt and vanilla extract in a large bowl until light and fluffy
Add melted butter and chocolate mixture into egg mixture and whisk until fully combined
Slowly add flour and cocoa powder into the chocolate batter and whisk until smooth
Pour the battering to the prepared cake pan and bake for 24-28 minutes for 9x9 pan or 22-24 minutes for 9x13 pan (avoid over baking so the center stays fudgy)
Let brownies cool in the pan (for easier cutting, refrigerate the brownies for 30 minutes to allow the fudgy center to set)
Cut the brownies into squares
Serve or store in airtight container