Prepare two 9-inch cake pans by greasing them well. Set aside. Preheat oven to 350 F for shiny metal pans, or 325 F for dark or nonstick pans.
Mix cake mix, flour, eggs, oil, and, milk in a large bowl. Beat with electric mixer set on medium speed (or beat vigorously by hand) for two minutes. Pour into the prepared 9-inch round cake pans.
Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean. Do not overbake. Remove from oven and allow to cool.
Remove cakes from pans. Using a serrated knife, split both layers in half horizontally, to end up with 4 layers.
Place layers on the plate of a cake stand or the plate part of a "cake saver" one at a time, spreading all but the reserved 1 cup of coconut mixture you made last night evenly between the layers.
Mix Cool Whip together with the reserved 1 cup coconut mixture. Frost sides and top of cake with this mixture. Cover the cake wit the top of the "cake saver" or another method (but not plastic wrap or anything that touches the cake) place in the refrigerator.
Do not remove, open, or eat for THREE DAYS. Do not even peek. The longer this cake sits in the refrigerator, the better it gets. However, it is not humanly possible to wait longer than three days. Store any remains in the refrigerator. Enjoy to the very last delicious crumb, hopefully within three additional days, for up to 6 days total.