Mix the cake mix according to directions on box. Bake in 2 cake layers and cool; split into 4 layers.
Mix 2 packages fresh frozen coconut with the sour cream and sugar. Set aside 1/2 c of this mixture for later use.
Spread the rest between layers. Now mix the 1/2 c mixture with the whipped topping; spread on top and sides. Refrigerate 3-4 days in an airtight container before cutting. Leave at least 3 days, 4 is better. Very moist.
Note: For a prettier presentation, toast about 1/2 cup of the coconut and sprinkle over top and/or sides.