Coconut Sour Cream Cake

1 pkg (18.25 oz) butter recipe cake mix 
1 container (16 oz) sour cream 
2 cups sugar 
4 cups sweetened flaked coconut 
1 ½ cups frozen whipped topping, thawed 

Preheat oven according to cake mix directions. Prepare cake mix according to package directions, using 2 (9”) round cake pans. Let cool as directed. Slice each cake layer horizontally in half, using a long serrated knife. While cake bakes, combine sour cream, sugar, and coconut in a bowl, stir well. Cover and chill 1 ½ hours. Reserve 1 cup sour cream mixture. Spread remaining sour cream mixture between cake layers. Fold whipped topping into reserved sour cream mixture. Spread on top and sides of cake. Place cake in an airtight container. Cover and chill at least 8 hours. Serves 12.