Preheat oven to 400 degrees. Grease and flour a baking sheet measuring 15.5x10.5x1 or equivalent size.
Sift flour, sugar, cocoa, and salt in a large bowl.
In a small pot, melt butter. Add water and salad oil. Mix and heat to a boil. Pour over dry ingredients and mix thoroughly.
Blend in buttermilk, eggs, baking soda, and vanilla. Pour into baking sheet. Bake for 20 minutes or until toothpick insert in middle comes out clean.
While brownies are baking, prepare frosting. Melt butter in a small pot on the oven.
Once it is melted, add cocoa and buttermilk. Mix and heat until it comes to a boil.
While your pot is heating up, combine powdered sugar and vanilla in a large bowl. Add heated mixture and blend until smooth.
Once brownies are done, pour over warm brownies. Use rubber spatula to spread to edges. Let cool completely before indulgence.