Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans with butter or cooking spray, then lightly flour them.

In a large mixing bowl, whisk together the granulated sugar, brown sugar, eggs, vegetable oil, and vanilla extract until smooth and creamy.

In a separate bowl, whisk together the all-purpose flour, baking soda, baking powder, cinnamon, and salt until evenly mixed.

Fold in the grated carrots and drained crushed pineapple into the wet mixture until just combined.

Gradually add the dry mixture to the wet ingredients, stirring gently until just combined.

If using, fold in the chopped walnuts now.

Divide the batter between the prepared cake pans and bake for 30-35 minutes, or until a toothpick comes out clean.

Let the cakes cool in the pans for about 10 minutes, then transfer to wire racks to cool completely.

Beat the cream cheese and unsalted butter together until smooth, then gradually add the powdered sugar until fluffy.

Stir in the vanilla extract and optional pineapple juice.

Once cooled, place one layer on a plate, frost the top, then place the second layer and frost the top and sides.

Decorate with additional walnuts or fresh pineapple slices, if desired.