Preheat your oven to 350°F (175°C). In a large mixing bowl, combine your favorite cake mix with the recommended ingredients according to the package instructions. Beat for about 2 minutes until smooth. Pour into a greased 9 x 13-inch baking pan and bake for 25-30 minutes, or until a toothpick comes out clean.

Remove the cake from the oven and let it cool on a wire rack for 1 to 2 hours.

In a medium bowl, mix together the sugar, sour cream, and thawed frozen coconut until fully blended and smooth.

Spread the majority of the coconut mixture over the cooled cake.

Combine the reserved coconut mixture with the whipped topping until smooth and fluffy.

Spread the whipped topping mixture over the coconut-filled cake evenly.

Refrigerate the cake for at least 4 hours or overnight to allow flavors to meld.