• Preheat oven to 350.
• Spray a jelly roll pan with non-stick cooking spray.
• In large mixing bowl, combine flour, sugar, baking soda, and salt. Set aside.
• In small mixing bowl, combine buttermilk, eggs, and vanilla. Set aside.
• In saucepan on medium heat, add butter, cocoa, water. Bring this mixture to a boil, stirring frequently.
• Add saucepan mixture to the large bowl of dry mixture. Mix to combine.
• Quickly add the wet ingredients and mix.
• Pour mixture into jelly roll pan. Bake 15-20 minutes or until toothpick comes out clean.
• Place on wire rack to cool and make the frosting.

For the frosting:

• Melt in a saucepan, butter, 4 tablespoons cocoa and 6 tablespoons buttermilk and stir to combine. Bring to a boil, stirring frequently.
• Add confectioners sugar and vanilla and stir to combine.
• Pour evenly over warm cake.
• Let frosting cool, then cut and serve.