Cake:
Preheat the oven to 350°F (175°C). Grease and flour three 8-inch round cake pans.
In a large mixing bowl, combine the white cake mix, eggs, buttermilk, and vegetable oil. Use an electric beater to mix on medium speed for 2 minutes until smooth.
Fold in the chopped pecans and shredded coconut.
Divide the batter evenly between the three prepared cake pans. Bake for 15-17 minutes or until a toothpick inserted into the center comes out clean.
Remove the cake pans from the oven and allow them to cool for 10 minutes. Then, transfer the cakes to wire racks to cool completely.
(Optional) If using rum, drizzle 1 tablespoon over each cake layer. Let it sit for 10 minutes to absorb.
Cream Cheese Frosting:
In a large bowl, beat the softened cream cheese and butter on medium speed until smooth and creamy.
Gradually add the powdered sugar, beating until fluffy.
Mix in the vanilla extract and fold in the chopped toasted pecans.
Assembly:
Once the cake layers are completely cooled, place one layer on a cake stand and spread a generous amount of cream cheese frosting on top.
Add the second layer and repeat, frosting the top and sides of the cake evenly.
Chill the cake for at least 2 hours before slicing and serving for best results.