Preheat your oven to 350°F. Grease and flour two 9-inch round cake pans (or use baking spray). Mix the cake according to the box directions — just add your water, oil, and eggs and beat for about two minutes. Scrape down the sides of the bowl halfway through to make sure everything is well combined. Divide the batter evenly between the two pans. If you see any air bubbles, give the pans a quick thump on the countertop to release them. Bake for 23–28 minutes, or until a toothpick inserted in the center comes out clean. You want this cake to be fully baked through since we're going to slice the layers in half later.

Cool and Freeze the Layers

Let the cake layers cool completely in their pans. You don't even need to remove them — just wrap them with plastic wrap right in the pans and pop them in the freezer. Leave them overnight, or at least long enough to freeze solid. This step is important because the cake is too tender to slice in half when it's fresh. Freezing it gives it the right consistency to cut cleanly. If you need to freeze them longer than overnight, wrap in plastic wrap first and then place in a freezer-safe bag for extra protection.

In a large bowl, mix together the 2 cups of granulated sugar, 1½ cups of sour cream, and 12 oz of coconut. I know sour cream sounds odd for a cake icing, but trust me — it's going to be delicious. Stir it well until everything is combined and the sugar is fully mixed in. This is honestly about the hardest part of the whole cake, just getting everything stirred together.

Split the coconut mixture roughly in half. One half stays as-is — that's your filling for between the layers. To the other half, fold in the 9 oz of thawed whipped topping until it's light and well combined. That becomes your outside frosting.

Take the frozen cake layers out of the freezer and remove the plastic wrap. Using a serrated knife, carefully slice each layer in half horizontally. Keep your hand on top and turn the cake as you cut, working your way to the center. You should end up with four thin layers total.

Place the first layer on your serving plate. Spread about one-third of the plain coconut filling (without the whipped topping) over the top. Add the second layer, flipping it so the cut side faces down into the filling — this lets the filling soak into that fresh-cut surface. Spread another third of the filling. Repeat with the third layer and use the remaining filling. Place the fourth layer on top.

Take the coconut mixture with the whipped topping folded in and spread it generously over the top and all the way down the sides. There's plenty of this mixture, so don't be shy with it. It creates a light, airy frosting that's not overly heavy. Sprinkle extra coconut all over the top so there's no question what kind of cake this is.

This is the part that requires a little patience. Cover the cake and refrigerate it for at least 24 hours before serving. You can let it sit for up to 3 days. This resting time lets all that coconut filling soak into the cake layers, and that's what makes it so incredibly moist and flavorful. Do not skip this step.