Preheat the oven to 350°F (175°C) and grease two 9-inch round cake pans.

In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, ground cinnamon, nutmeg, and salt.

In a separate bowl, whisk together the granulated sugar, large eggs, and vegetable oil until smooth.

Fold in the shredded carrots and well-drained crushed pineapple into the wet mixture.

Pour the dry ingredients into the wet mixture, and fold together until just combined.

If using walnuts, gently fold them into the batter.

Divide the batter evenly between the prepared cake pans and smooth the tops.

Bake for 30 to 35 minutes, checking for doneness with a toothpick.

Remove the cakes from the oven and let cool in the pans for about 10 minutes before inverting onto wire racks.

In a mixing bowl, beat the cream cheese and unsalted butter until creamy, then gradually mix in powdered sugar and vanilla.

Once the cake layers are completely cooled, assemble with cream cheese frosting between and on top of the layers.