Preheat oven to 325 degrees Fahrenheit and line 8×8-inch baking pan with parchment paper with 2-inch overhang on 2 sides. Set aside.
Using stand mixer, whip eggs, sugar, vanilla extract, and salt on medium speed for about 2 – 3 minutes or until mixture is fluffy and pale and when you lift up the mixer head, the batter falls back in thick trails like a ribbon.
Slowly mix in butter.
Sift together flour and both cocoa powders and fold into batter until just combined.
Pour batter into baking pan and bake for 30 – 35 minutes, or until toothpick inserted in center comes out mostly clean with some wet crumbs. Thermometer inserted into center should read 195 degrees Fahrenheit. Immediately sprinkle with sea salt.
Allow brownies to cool in pan for at least 30 minutes before removing by lifting out using overhanging parchment paper.