Grease and flour two 9 inch pans. Prepare cake mix as directed by manufacturer, Bake according to instructions on package. When cake is cool, remove from pans and cut in half, horizontally.
To make the filling, mix together the sour cream and sugar in a medium sized bowl. and the cream of coconut (I use 1/2 can some people only use 2/3s, stir in 1 1/2 cups of the coconut. reserve 1 cup of this mixture and spread the rest between the cooled cake layers. Fold whipped topping into the remaining filling, frost the outside of the cake. Sprinkle the remaining coconut over the top of the frosted cake.
Refrigerate from 1 to 3 days before serving.
But if need be you can serve same day