Prepare cake mix as directed using the 3 eggs, 1 1/4 cup of water and 1/2 cup of butter, then pour into 8" or 9" pans. **depending on what brand of cake mix you buy the amount of eggs, butter, water may be different - just use the ingredients listed on your box of yellow cake and omit any of mine that aren't needed. I used Betty Crocker butter recipe yellow, but it doesn't not matter which one you use**.
Meanwhile, mix together the sugar, coconut and sour cream.
Set aside 1 cup of the coconut mixture.
After the cake has cooled split the layers using a serrated knike, so you have 4 layers.
On a covered cake dish begin layering the cake with the coconut mixture, leave the top layer unfrosted.
Take the remaining cup of coconut mixture and mix with the cool whip.
Frost the top and the sides of the cake.
Cover the cake and refrigerate for 3 days before serving.