Preheat oven to 350 degrees. Grease and flour a 9x13 pan.
Combine flour and sugar in large mixing bowl. In saucepan,
melt butter, add cocoa, and cola heat to boiling point. Cool
slightly. Pour over flour and sugar mixture, stir until well
blended. Add buttermilk, beaten eggs, soda and vanilla. Mix
well. Stir in marshmallows. Pour in pan and bake 40 minutes
or until toothpick comes out clean. Frost while cake is still
For frosting: combine butter, cocoa and cola in saucepan.
Heat to boiling, pour over powdered sugar and mix well. Stir
in nuts and frost cake.