From start to finish, plan on spending about an hour and 15 minutes on this cake if you rush the cooling time for the cake a little bit.
Preheat the oven to 350ºF. Grease and flour a 9-x13-inch pan.
Combine the flour, sugar, and baking soda in a large bowl. Combine the water, butter, shortening, and cocoa in a saucepan. Bring the mixture to a boil over medium heat, stirring frequently. Pour the cocoa mixture into the flour mixture and beat until blended. Add the buttermilk, eggs, and vanilla and beat until well blended. Pour the batter into the prepared pan and bake until a toothpick inserted into center comes out clean, about 30 minutes. Cool the cake completely in the pan and ice with <a href="http://www.emerils.com/recipedb/recipepull.php?id=3386" target="_blank">Your Father’s Day Cake Icing</a>. Cut into squares and serve.