Bring 1/2 cup butter, oil, water, 3 tbsp cocoa and a sprinkle of salt to a boil in a medium sized pan. Stirring regularly.
Once mixture is boiling, remove from stove and stir in flour, baking soda, vanilla, sugar, eggs, and buttermilk and pour onto your greased jelly roll pan. Bake for 15 minutes or until cake barely springs back when touched with a finger.
For the Frosting
Bring 1/2 cup butter, 1/4 cup cocoa, powdered sugar and milk to a boil on the stove, stirring regularly. Pour over lightly cooled cake.