1. Combine sugar, sour cream and coconut, blend well, then chill for about 2 hours. Put 1 cup of the mixture aside for the frosting.
2. Prepare the cake mix according to the package. Bake in two 9 inch round cake pans. When the cakes have cooled completely, split each cake in two, for a total of 4 layers.
3. Spread sour cream mixture between all layers, but not on top. Use the 1 cup of mixture saved earlier and mix with Cool Whip. Spread this over top and sides. Then seal cake in container and refrigerate for 3 days before serving. ENJOY