My mother made this cake for Easter almost every year growing up. She would make this icing & frost home-made butter cake. Here is how she did it..
Combine POWDERED sugar, sour cream, whipped topping & 1 tsp vanilla extract. Fold in coconut. Frost cake. KEY STEP! Seal in airtight container & refrigerate for 3 days!
This is one cake I can close my eyes & almost taste. The 3 days allows the frosting to somewhat soak into the layers making it so moist & delicious!

I make this frosting often.. Usually I mix granulated sugar, sour cream, and coconut and chill in refrigerator, while you bake cake.. Then FOLD IN COOL WHIP GENTLY.. OH and the frozen coconut must be defrosted all the way... On its own. Not in microwave. I leave out on cabinet. After the cake is frosted leave it in fridge..

Wish you had stated if it's XXX confection sugar or granulated sugar for the icing

If only half carton of cool whip is used the frosting is perfect.

Just wonderful....and yes it freezes well

Can you freeze this coconut sour cream/cool whip cake?

It won't be runny if you do this... Whip sugar into sour cream until the sugar is dissolved then you need to take a rubber spatula and very gently and slowly FOLD the cool whip into the sour cream mixture. Whipping, beating or using electric mixer in the last step will result in runny icing. Also do not use light or fat free ingredients or you will get more of a gloppy texture.Best also to use name brand Cool whip.

You are right on target with your suggestions about the icing. I do the same thing. Folding gently is the answer, but I can use granulated sugar (not finely granulated) and it works well. Only use sugar to taste and not what most recipes call for. Thanks for your answer.

Try using powdered sugar instead of granulated.

This recipe tastes amazing, however I have had trouble with cool whip being too runny to stack! I have tried it several times, and every time the cake ends up in a bowl!! But gets rave reviews!

I've made this recipe for over 30 years! Only difference is I mix in Cool Whip for top and side of cake... the inbetween layers I use just sugar and sour cream.

Another tip... mix sugar and sour cream together a day ahead... I also will use more sour cream for richer icing.