Lightly beat 2 eggs and add to cake mixture as well as vanilla. Mix well and pour in prepared pan. Bake at 350 degrees for 30-35 minutes or until knife or toothpick comes out clean. Do not cook more than 35 minutes though because you want cake to be moist. Allow cake to completely cool before icing.
In a medium boiler, add butter, cocoa and coca cola. Heat on medium heat until butter melts and mixture starts to boil. Only boil for about 15-30 seconds and remove from heat. Add in confectioners sugar and mix well to get out any lumps and icing reaches desired consistency.