Preheat your oven to 350°F (175°C). Line a 10×15-inch jelly roll pan (sheet pan) with parchment paper and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, combine the granulated sugar, vegetable oil, vanilla extract, and eggs. Beat on medium speed for about 3 minutes, or until the mixture becomes pale yellow and slightly thickened.
In a separate medium bowl, whisk together the flour, ground cinnamon, nutmeg, baking soda, and kosher salt until well combined.
With the mixer on low, slowly add the dry ingredients to the wet mixture. Mix only until incorporated, taking care not to over-mix the batter.
Remove the bowl from the stand mixer. Using a spatula, gently fold in the chopped walnuts, finely grated carrots, and drained crushed pineapple. Stir just until all ingredients are evenly mixed throughout the batter.
Transfer the batter into the prepared pan, spreading it into an even layer to ensure consistent baking.
Bake for 24 to 28 minutes, checking for doneness starting around the 22-minute mark. Insert a toothpick into the center of the cake—if it comes out with just a few moist crumbs (but no raw batter), it’s done.
Allow the cake to cool completely in the pan before applying the frosting.
Maple Frosting
In a large mixing bowl, combine the softened butter, maple syrup, and maple extract. Using a hand mixer or a stand mixer with the paddle attachment, beat on medium speed until smooth and creamy.
Gradually incorporate the confectioners’ sugar, adding about ½ cup at a time. Mix well after each addition, continuing until the frosting reaches your preferred consistency—thick, smooth, and spreadable. Adjust the sugar amount depending on how sweet and creamy you like your frosting.
Once the cake has completely cooled, spread the maple frosting evenly across the top. Use a spatula to smooth it out, or pipe decorative swirls for a more polished presentation.
Finish with a sprinkle of chopped walnuts on top, if desired. Slice and serve.