Preheat your oven to 175°C (350°F). Lightly grease a 9×13-inch pan and dust it with flour to prevent sticking.
In a medium bowl, combine flour, baking powder, baking soda, cinnamon, and salt. Give it a quick whisk so everything is evenly blended.
In a larger bowl, whisk sugar, eggs, oil, and vanilla until smooth and slightly glossy.
Slowly add the dry mixture into the wet mixture. Stir gently—don’t overmix or the cake can turn dense.
Fold in the carrots, pineapple, and walnuts. The batter will look thick and textured—that’s exactly what you want.
Pour the batter into your prepared pan. Bake for 35–40 minutes. Check with a toothpick—if it comes out clean, you’re good to go. Let the cake cool completely before frosting.
Beat cream cheese and butter until smooth and creamy. Add icing sugar and vanilla, then whip until fluffy.
Spread frosting evenly over the cooled cake. Top with pineapple pieces or carrot shreds if you’re feeling fancy.