Make filling first:

16 oz. frozen coconut
2 c. sugar
2 c. sour cream

Mix well and let stand in refrigerator overnight.

CAKE:

1 pkg. yellow Duncan Hines cake mix
1 stick butter, softened
4 eggs
1 c. water

Blend cake mix, butter, eggs and water. Bake in two layers at temperature recommended on box. Cool layers and split, making four layers. (Do NOT cook in four layers.) Frost cake and refrigerate. Best when served third or fourth day.