Preheat the oven to 350º Fahrenheit. Grease with shortening, then dust with flour 2 8” round cake pans.
In the bowl of a stand mixer, add the cake mix, milk, eggs and vegetable oil. Beat on medium speed for 2 minutes, scraping the sides of the bowl as needed.
Divide the batter equally between the two prepared cake pans.
Bake for 25-27 minutes or until the center of the cake bounces back when you touch it.
Allow the cakes to cool for 5 minutes in the pan, then turn them out on a wire rack to cool completely.
While the cakes are cooling, prepare the filling. In a medium bowl, combine the sour cream, sugar and thawed coconut. Mix well. Place this into the refrigerator until you are ready to assemble the cake.
To assemble the cake, cut each cake into two layers. You should now have four layers.
Place one cake layer down on a cake plate, cut side up.
Scoop 1/2-2/3 cup of the coconut filling into the center of the cake. Spread to the edges carefully so that it does not run over.
Place another cake layer on top and then spread another 1/2-2/3 cup filling on top.
Repeat with another cake layer and more filling.
Then place the last cake layer on top.
In a bowl, fold together any remaining sour cream filling (we had about ½ cup left over) with the 8 ounces of Cool Whip.
Use this Cool Whip mixture to frost the outside and top of the cake.
Store in the refrigerator for 3 days before serving. This allows the cake to develop the best flavor.