1. Preheat oven to 300 degrees F (150 degrees C). Line one 9x13 inch pan with greased parchment paper. 2. Combine the cocoa, melted butter, sugar, eggs, salt , flour and vanilla. Mix until well combined. It should be very thick and sticky. 3. Spread mixture into the prepared pan. Bake at 300 degrees F (150 degrees C) for 30 minutes. Cool completely before cutting into squares.