Prepare cake mix as per package directions for a two layer round cake. Once cake is cool split layers with a thread to create four layers. Mix together sour cream, sugar and all but 1/2 cup of the coconut. Set aside one cup of the sour cream/coconut mixture. Spread remainder between layers of cake. In a large bowl, stir together whipped topping and reserved sour cream/coconut mixture; use this to frost the cake. Toast the remaining 1/2 cup coconut and sprinkle over cake. Refrigerate for up to 3 days before serving.
I don't recall the exact recipe I used, but this one is similar. But I know, I didn't use sour cream. And the addition of the coconut on the exterior, was partially accidental.
I have made this cake for years.....it's a hit with anyone who enjoys coconut!!