Preheat oven to 325. Grease a 8x8 glass or light metal pan.
In medium bowl add butter. In double broiler, on medium heat, melt the butter.
Slowly add cocoa powder stirring continually.
Add vanilla, salt, and sugar one at a time and continue stirring.
Remove from heat. Add eggs one at a time. Stir well to make sure it is fully emulsified.
Add flour a little at a time and beat in until fully incorporated (about 30-40 strokes).
Transfer to greased 8x8 dish. Using a spatula, work batter towards the edges until evenly spread.
Bake for 25 to 30 minutes.