Bake a 2 layer cake according to directions on box.
Split cake into 4 layers.
Mix sugar, sour cream and coonut.
Reserve 1 cup mixture for icing.
Put sugar-coconut mixture between layers.
Mix 1 cup reserved mixture with cool whip and spread on top and sides of cake.
Regridgerate for 3 days in an air-tight container.
Keep cake in refrigerator until finisherd_ which won't be long.