Cake: Preheat oven to 350 degrees F. Grease a 13 x 9-inch pan. Sift together flour and sugar; set aside.
Bring oleo, cocoa and Coke to a boil and add to flour and sugar mixture.
Add buttermilk, soda, vanilla and eggs to above mixture and mix well. This will be quite thin. Pour into well greased pan, 9 x 13 inch. Bake at 350 for 30 minutes.
Icing: Bring oleo, cocoa and cake to a boil. Add sugar and vanilla and mix well. Then add nuts and marshmallows and mix well. Frost while cake is warm.