Texas Sheet Cake

Yay summer! I made this for a pool party. Usually, it's smooth on top, but it shifted on the ride over. Still delicious.
Cake:

2 cups sugar

2 cups flour

4 tablespoons cocoa

2 sticks butter

1 cup water

1 cup buttermilk

1 teaspoon vanilla

1 teaspoon baking soda

2 beaten eggs

Preheat oven to 350 degrees F. Place sugar and flour in a bowl. Place cocoa, butter, and water in a saucepan and bring to a boil. Add the cocoa mixture to the flour mixture, and mix well. Add the rest of the ingredients and mix thoroughly. Pour batter into a 17x12 inch sheet pan (I used a 15x10) and bake at 350 for 15 to 20 minutes.

Icing:

4 tablespoons cocoa

6 tablespoons milk

1 stick butter

16-ounce box powdered sugar

Place powdered sugar in a mixing bowl. Bring cocoa, milk, and butter to a boil in a saucepan. Add cocoa mixture to the powdered sugar and mix well to remove the lumps. Pour icing over warm cake and let cool.