Preheat oven to 350°F. Prepare cake according to package directions, and bake in a greased 13x9 inch baking dish.
While the cake is baking, whisk together the cream of coconut and sweetened condensed milk.
While the cake is still warm from the oven, use a skewer, drinking straw, or fork to poke holes in the cake about 1 inch apart.
Pour the milk mixture over the top. Refrigerate until cool, about 1–2 hours.
Spread whipped topping over the top and sprinkle with coconut. Refrigerate until ready to serve.
Store cake in the refrigerator.
Notes
Cream of coconut is NOT the same as coconut milk. Cream of coconut (or crema de coco) is quite sweet, and you cannot substitute coconut milk in its place. You need a can of "cream of coconut" for this recipe (Goya is one brand that makes it). You can use homemade whipped cream in place of the whipped topping, if you'd like. Whip 2 cups of heavy cream with 2 tablespoons powdered sugar and 1 teaspoon vanilla extract until light and fluffy, and use in place of the whipped topping.Store any leftover cake in the refrigerator, or freeze it (wrapped tightly or in a freezer-safe container) for up to 2 months. Defrost in the refrigerator.