Preheat your oven to 350°F. Lightly grease three 9-inch round cake pans (or two if you prefer thicker layers) and line the bottoms with circles of parchment paper. Dust the sides lightly with flour, shaking off any excess.

In a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, combine the dry cake mix, dry instant vanilla pudding mix, eggs, buttermilk, oil, and vanilla extract.

Beat the mixture on medium speed for exactly 2 minutes until the batter is smooth, thick, and completely integrated.

Stop the mixer and use a rubber spatula to gently fold in the 1 cup of flaked coconut and 1 cup of chopped toasted pecans until they are evenly distributed through the cake matrix.

Divide the thick batter equally among your prepared cake pans, smoothing the tops flat with an offset spatula.

Place the pans on the middle oven rack and bake at 350°F for 15 to 18 minutes (or 25 to 30 minutes if using a standard 9x13-inch sheet pan). The cake is finished when the tops spring back lightly when touched and a toothpick inserted into the center comes out clean.

Remove the pans from the oven and let the cake layers cool flat on wire racks for 10 minutes. Run a thin knife around the inside edges, carefully turn the cakes out onto the racks, peel off the parchment paper, and allow them to cool down completely to room temperature.

While the layers cool, prepare the frosting. In a medium bowl, beat the softened cream cheese and unsalted butter together with an electric hand mixer for 2 minutes on high speed until light, fluffy, and free of lumps.

Reduce the mixer speed to low and gradually add the sifted powdered sugar one cup at a time, followed by the vanilla extract. Once incorporated, turn the mixer to high and whip for 1 to 2 minutes until a silky, spreadable frosting baseline forms. (Add heavy cream a teaspoon at a time if the frosting feels too stiff).

To assemble, place your first cooled cake layer flat on a serving plate or cake stand. If using, brush the surface lightly with 1 tablespoon of the rum or simple syrup. Spread roughly ¾ cup of cream cheese frosting uniformly across the layer.

Repeat the process with the remaining cake layers. Use the rest of the frosting to heavily coat the top and outer sides of the entire cake.

Heavily press extra chopped pecans and shredded coconut into the fresh frosting around the sides and top border of the cake for a classic finish. Place the assembled cake into the refrigerator to chill for at least 2 hours before slicing to allow the moisture to distribute evenly and the layers to set securely.