Creating Hawaiian Carrot Pineapple Cake is straightforward if you follow these simple steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
2. Mix Dry Ingredients: In a large bowl, combine the flour, sugar, baking soda, baking powder, cinnamon, and salt. Whisk until well blended.
3. Combine Wet Ingredients: In another bowl, whisk together the oil, eggs, grated carrots, crushed pineapple, and vanilla extract until fully combined.
4. Combine Mixtures: Gradually add the wet mixture to the dry ingredients, stirring gently until just combined. Be careful not to overmix.
5. Add Walnuts: Fold in the chopped walnuts if using, ensuring they are evenly distributed throughout the batter.
6. Divide Batter: Pour the batter evenly into the prepared cake pans.
7. Bake: Place in the preheated oven and bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.
8. Cool: Remove the cakes from the oven and allow them to cool in the pans for about 10 minutes. Then, transfer them to wire racks to cool completely.
9. Prepare Frosting: In a mixing bowl, beat together the softened cream cheese and butter until creamy. Gradually add the powdered sugar, mixing until smooth. Stir in the vanilla extract.
10. Frost the Cake: Once the cakes have cooled, spread a layer of cream cheese frosting on top of one cake layer. Place the second layer on top and frost the top and sides of the cake.