Preheat oven to 375 degrees. Grease a 9x13 inch cake pan.
Put oil and water in a saucepan and bring to a boil. Put flour and sugar in a mixing bowl. Pour the hot oil/water over the sugar and flour. Beat together good with a spoon. Stir in the eggs, vanilla, baking soda, buttermilk and cocoa. Pour into a greased pan. Bake for 20 to 25 minutes.
While cake is baking, make icing:
1/2 stick butter
3 tbsp milk
2 tbsp cocoa
1/2 tsp vanilla
1/2 box powdered sugar
1/2 cup chopped nuts (optional)
Bring butter, milk and cocoa to a rapid boil. Remove from heat and add vanilla, powdered sugar and nuts. If you want more icing just double the recipe.