Preheat the oven according to package directions. Grease a 9x13-inch baking dish.
Prepare the white cake mix according to package instructions and pour it into the baking dish that has been prepared before.
Bake as guided on the package, or until a toothpick that is inserted in the center comes out clean.
Using a fork, poke holes all over the warm cake, spacing them out evenly.
In a medium bowl, mix together sweetened condensed milk and cream of coconut until well combined.
Pour the coconut mixture over the cake, using a spatula to spread it evenly over the entire surface.
Cover and refrigerate for at least 4 hours or overnight.
Spread thawed whipped topping over chilled cake and sprinkle with flaked coconut.
Cover and store in the refrigerator until ready to serve.
