Preparation Steps

• Position a rack in the middle of the oven and preheat to 350°F. Line a 9x13-inch (23 x 33 cm) metal baking pan with parchment, leaving an overhang on the long sides for easy removal; lightly oil the paper.
• In a large mixing bowl whisk together the oil, granulated sugar, and brown sugar until smooth. Whisk in the eggs one at a time until fully incorporated, then stir in the orange zest if using.
• In a separate bowl combine the flour, baking powder, baking soda, salt and cinnamon. Stir the dry mix a few times with a fork to distribute evenly.
• Add the dry ingredients to the wet mixture in two additions, folding gently with a rubber spatula until just combined — avoid overmixing. Fold in the shredded carrots until they’re evenly dispersed.
• Transfer the batter to the prepared pan and spread to an even thickness. Tap the pan once on the counter to release large air pockets. Bake for 28–32 minutes, or until the top is set and a toothpick inserted in the center comes out with a few moist crumbs.
• Remove the cake from the oven and let it cool in the pan on a wire rack for 15 minutes. Use the parchment overhang to lift the cake out and set it on the rack to cool completely — chilling the cooled cake 20–30 minutes makes frosting and slicing much neater.
• While the cake cools, make the frosting: cut the cold cream cheese and mascarpone into chunks and place in a chilled bowl. Using a hand mixer on low, beat just until smooth. Add the sifted powdered sugar and vanilla and beat on medium-low until creamy and slightly fluffy — take care not to overbeat or it will become too loose.
• If you plan to pipe decorations, transfer about 1/2 cup of frosting to a small bowl and tint with gel colors as desired; chill that portion 10 minutes to firm it slightly before piping. Spread the remaining frosting over the cooled (or lightly chilled) cake with an offset spatula.
• Use a piping bag fitted with a small round or star tip to pipe carrot shapes with orange frosting and tiny green tops, or simply grate a little carrot and scatter on top for a rustic finish. Keep the cake refrigerated if not serving immediately.
• Slice into 12 squares and serve chilled or at cool-room temperature. Store leftovers covered in the refrigerator for up to 3 days.