Preheat oven to 350°F (175°C). Grease an 8-inch square baking pan.
In a medium bowl, whisk together the flour, cocoa powder, and salt. Set aside.
Place the melted butter and sugar in a large mixing bowl. Using a spoon, mix until combined. Add the eggs and vanilla extract, and stir until well mixed.
Add the flour mixture in three portions, mixing just until the batter is combined.
Transfer the brownie batter to the prepared pan. Use a spatula to spread the batter evenly in the pan.
Bake 25 to 30 minutes, or until a pick inserted into the center of the brownies comes out with moist crumbs.
Cool the brownies for at least 15 minutes before cutting into bars.
Notes
*Either natural or Dutch process cocoa powder will work. Just be sure to use a good quality cocoa powder. There are several brands of dark cocoa powder available. For these brownies, I used King Arthur Flour's Double Dutch Dark Cocoa.