Coconut Mounds Cake

Preparation : Mix and bake cake mix as directed for two layers. Let layers cool then split each one in half lengthwise. In a saucepan over medium heat mix together the white sugar, margarine, and 1/2 cup of the evaporated milk. Cook for 10 minutes. Stir in the marshmallows and mix until smooth. Stir in the coconut. Spread the filling between the cake layers. Mix together the cocoa, remaining 1/4 cup evaporated milk, the confectioner's sugar, and the vanilla. Beat until smooth and spread over top and sides of cak