Preheat and Prep: Preheat your oven to 350°F (175°C). Grease and flour three 9-inch round cake pans and set aside.

Mix the Batter: In a large mixing bowl, beat the white cake mix, eggs, buttermilk, and vegetable oil at medium speed with an electric mixer for about 2 minutes, or until the batter is smooth and well combined.

Fold in the Mix-ins: Gently stir in the flaked coconut and the ⅔ cup of toasted pecans until evenly distributed throughout the batter.

Bake: Pour the batter evenly into your prepared 9-inch round cake pans. Bake at 350°F for 15 to 17 minutes, or until a wooden toothpick inserted into the center of the cakes comes out clean.

Cool: Allow the cakes to cool in their pans on wire racks for 10 minutes. Afterward, carefully remove the cakes from the pans and transfer them directly to the wire racks to cool completely.

Add the Rum (Optional): Once cooled, sprinkle each cake layer evenly with 1 tablespoon of rum (if using). Let the layers stand for 10 minutes to absorb the flavor.

Make the Frosting: In a large bowl, beat the softened cream cheese and butter at medium speed with an electric mixer until completely smooth and creamy. Gradually add the powdered sugar, beating until the mixture is light and fluffy. Finally, stir in the vanilla extract and the 1 cup of toasted pecans.

Assemble and Frost: Place one cake layer on your serving plate, spread a layer of frosting over the top, and repeat with the remaining layers. Frost the top and the sides of the cake evenly.

Chill and Serve: Chill the frosted cake in the refrigerator for at least 2 hours before slicing. Enjoy!