Preheat the oven to 355F (180C) and line an 8" by 8" (20cm by 20cm) brownie pan with parchment paper so the bottom and sides are covered.

In a bowl, sift the flour, cocoa powder, and salt. Set aside.

In the bowl of a stand mixer (or you can use a large mixing bowl and a hand mixer), add the eggs, sugar, and vanilla extract. Whip on medium-high for 5 minutes or until fluffy and tripled in volume.

Add the chocolate mixture to the egg mixture while the mixer is running on low until fully incorporated. Then, fold in the dry ingredients just until fully incorporated (you can do this with the mixer as well or use a rubber spatula).

Pour the batter into the prepared pan and tap it against a flat surface to burst the air bubbles in the batter.

Bake for 40-45 min (cover loosely with a piece of foil if the top browns too fast and keep baking), or until the toothpick inserted into the edge comes out clean or with a few crumbs and the middle has set. A toothpick inserted in the center will come out a bit wet or with a few wet crumbs. You can also check the internal temperature in the middle which should be 180F-190F (82C-88C).

Remove from the oven and let it cool down in the pan for one hour. Then, lift up holding the parchment paper and place the brownie on a cooling rack to cool down completely.

Refrigerate for an hour, then cut into 9-12 even pieces and serve.