Pre heat oven to 350 degrees. Grease and flour a 13by9-inch baking pan.
Combine the sugar and flour in a large mixing bowl. Bring the butter, oil, cocoa,and the 1/4 cup water to a boil in a saucepan. ADD to the flour mixture.
Beat together the eggs, baking soda, buttermilk, and vanilla. Add to the chocolate mixture, mix well and pour into the prepared pan. Bake 25 minutes
WHILE cake is baking, make the icing by melting the bitter in the cocoa and milk over low heat. Bring mixture to a boil, then remove from the heat. Stir in the confectioners' sugar. Slowly mix in the nuts and the vanilla. Take the cake from the oven, and when it cools a bit cover with the marshmallow creme. Pour the warm icing over the cake and marshmallow creme. Cool the cake before serving.