Preheat the oven to 325°F. Line the bottom and sides of an 8-inch square baking pan with parchment paper.

Combine the butter, sugar, cocoa, and salt in a medium heatproof bowl and set the bowl over a saucepan with a bout 2 inches of simmering water. Stir occasionally until the butter is melted and the mixture is smooth and warm, but not hot.

Whisk in the eggs one at a time, stirring rapidly after each one. When the batter is completely blended add in your flour of choice and mix until just combined. Spread evenly into prepared pan.

Bake until a toothpick pushed into the center comes out slightly moist with flecks of brownie 20 to 25 minutes.