Awesome Brownie Cake

Brownie:
1/2 cup butter
1/2 cup oil
1 cup water
4 tablespoons unsweetened cocoa
2 cups flour
2 cups sugar
2 eggs
1 teaspoon baking soda
1/2 cup buttermilk
1 teaspoon vanilla

Frosting:
1/2 cup butter
3 tablespoons unsweetened cocoa
1/3 cup buttermilk
1 packet confectioners' sugar
1 cup chopped walnuts
1 teaspoon vanilla

Preheat oven to 350-degrees. Grease and flour a 9 x 13-inch baking pan. Mix butter, oil, water, and cocoa together in small saucepan. Bring to boil. Add mixture to flour and sugar and beat until smooth. Add eggs, baking soda, buttermilk, and vanilla. Mix well. Pour into prepared baking pan. Bake 20 minutes. Frosting: Put all frosting ingredients in medium saucepan and heat. Do not boil. Frost immediately after removing from oven. Cut into squares when cool.