Preheat the oven to 350 degrees Fahrenheit. Spray a 11 x 15 inch pan with nonstick spray and set aside.

In a large mixing bowl combine all-purpose flour, granulated sugar and salt. Mix until combined. Set aside.

In a medium size saucepan combine the butter, cocoa, vegetable oil and water. Turn heat to medium-high, stir constantly while it comes to a boil, remove and pour over the dry ingredients in the large mixing bowl. Stir to combine.

Add buttermilk, eggs, baking soda and vanilla extract to the bowl. Stir to combine.

Pour brownie mixture into the prepared pan. Bake in a preheated oven at 350 degrees Fahrenheit for 22-27 minutes or until brownies test done.Remove from the oven.

Immediately make frosting by combining buttermilk, cocoa, and butter in a medium size saucepan. Bring to boil over medium-high heat while stirring constantly. Remove and add in powdered sugar, 2 cups at a time, stirring in between additions.

Pour frosting over bars while still warm. Let brownies cool and frosting set.