Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or line them with parchment rounds.

In a large bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon until evenly combined.

In a separate bowl, whisk the oil and eggs until smooth and slightly thickened. Stir in the vanilla.

Add the grated carrots and the well-drained crushed pineapple to the wet mixture. Stir so everything is coated evenly.

Pour the wet ingredients into the dry. Stir gently with a spatula until just combined and no streaks of flour remain. Fold in the nuts if using.

Divide the batter evenly between the prepared pans and smooth the tops. Tap the pans lightly to remove large air bubbles.

Bake for 25 to 30 minutes, rotating the pans halfway through. A toothpick inserted in the center should come out clean or with a few moist crumbs.

Let the cakes cool in the pans for 10 minutes. Run a knife around the edges, then invert onto a wire rack. Cool completely before frosting.

When fully cool, spread or pipe cream cheese frosting on one layer, stack the second layer, and finish the top.

Serve at room temperature.