Preheat your oven to 350°F and line a 9x13-inch baking dish with parchment paper.
In a large bowl, combine the butter and sugars (brown and white), mixing until well blended.
Add the eggs and vanilla extract, then beat until the mixture becomes light and fluffy.
Shred the carrots, pat them dry with a paper towel, and stir them into the wet ingredients until evenly incorporated.
Add the flour, spices, baking soda, salt, and cornstarch, then fold together just until combined.
Transfer the dough to the prepared baking dish, pressing it into an even layer.
Bake at 350°F for 13-18 minutes, checking for doneness.
Allow the bars to cool completely before frosting.
In a stand mixer or with a hand mixer, beat the softened butter and cream cheese together until fluffy.
Add the rest of the frosting ingredients and whip until smooth.
Once the bars are fully cooled, lift them out of the dish using the parchment paper.
Spread the cream cheese frosting evenly over the top.
Lastly, sprinkle the frosted bars with a light dusting of cinnamon before cutting into 12 even squares to serve.
Notes
Sandy’s tips:
Storage: Store leftover carrot cake bars in an airtight container in the fridge for up to 5 days due to the cream cheese frosting. The flavors deepen over time! Unfrosted carrot cake bars can be stored in an airtight container at room temperature for 2-3 days.
Freeze and make-ahead: Wrap unfrosted carrot cake bars in plastic and foil for up to 3 months. Thaw the cake bars overnight in the fridge and allow them to sit at room temperature for about 15 minutes before adding fresh cream cheese frosting.
Cool before frosting: Make sure that the cake bars have cooled completely as any residual heat and steam will make the frosting runny.
Parchment overhang: Line the baking dish with parchment paper, leaving an overhang on two opposite sides to easily lift the baked bars out for frosting and cutting.
Soften the butter and cream cheese: These two ingredients must be left out to soften for a smooth, well combined frosting. Pop them in the microwave for short bursts of time if you forgot to soften them at room temperature but be careful not to melt them.
How to grate/shred the carrots: Wash and peel the carrots first. Then, use a box grater to grate the carrots. A grater attachment on a food processor is also an option.