In a large mixing bowl (or in a stand mixer), add the butter and shortening and cream on slow speed until smooth.
Pour in the granulated white sugar. Continue to cream mixture until smooth.
Next, add the eggs and vanilla extract. Mix until well combined.
In a separate bowl, mash the overripe bananas, then combine with the crushed pineapple and crushed nuts.
Add the banana, pineapple, and nut mixture into your large mixing bowl and stir.
In a separate bowl combine the sifted flour, salt, cinnamon, and nutmeg.
Now, alternate adding the dry ingredients and wet ingredients, adding small amounts of buttermilk in between. Mix using a handheld mixer or stand mixer on medium speed.
Next, grab three 9-inch cake pans. Grease with butter or baking spray, or line with parchment paper.
Bake each cake for 30 minutes on 350 F until done (use a toothpick to test for doneness).
Remove the cakes from the oven and let them sit for 15 minutes before removing them from the pan.
Remove the cakes from the pans and let the cakes cool completely on wire cooling racks.