In a large bowl put flour, sugar, soda, salt, and cocoa. Bring the butter, Crisco, and water to a boil and add to the dry ingredients. Beat until well mixed. Add buttermilk, eggs, and vanilla. Beat until well mixed. Put in 9x13 pan. Bake 30 minutes at 400 degrees. The cake is very good without frosting; maybe sprinkle with some powdered sugar.