Preheat oven to 325 degrees Fahrenheit and grease a 9"x13" cake pan.

In the bowl of an electric mixer, mix together oil, vanilla, sugar, and eggs. Mix well.

In a separate bowl, stir together flour, baking soda, baking cocoa and salt. Next, alternately add to the wet mixture the buttermilk, boiling water and flour mixture (starting with the flour mixture), mixing in between each addition. Be sure to scrape down the sides and bottom of the bowl to make sure everything is getting incorporated.

Pour batter into prepared cake pan and bake for approximately 40 minutes, or just until a toothpick inserted into the center comes out clean.

Let the cake cool for about half an hour, then carefully poke holes into the top of the cake with a fork so it will absorb some of the icing.

Prepare the icing by stirring together butter, milk, vanilla and baking cocoa in a saucepan over the stovetop on medium high heat. Stir constantly until boiling. Immediately remove from heat and stir or whisk in powdered sugar. Stir well. Immediately pour icing over cake. Add sprinkles if desired.