1. Preheat the oven to 325°F. Line a 9×13-inch pan with parchment paper. If using flower nails, place 2 to 3 in the center of the pan and spray them with nonstick baking spray.

2. In a large bowl, combine the brown sugar, granulated sugar, and oil.

3. Whisk in the eggs until the batter is smooth.

4. Sift together the flour, baking soda, baking powder, salt, cinnamon, nutmeg, and cloves in a separate bowl.

5. Add half of the dry ingredients to the egg mixture and mix until combined.

6. Add the buttermilk and mix until combined.

7. Mix in the remaining dry ingredients until just combined.

8. Fold in the finely grated carrots.

9. Pour the batter into the prepared pan. If using flower nails, press them down against the bottom of the pan.

10. Bake for 40 to 45 minutes, until a toothpick comes out with a few moist crumbs.

11. Leave the cake in the pan on a wire rack to cool completely. To speed this up, place the pan in the freezer for about 45 minutes.

12. For the frosting, beat the butter and cream cheese on medium speed with a paddle attachment for 30 seconds, until smooth.

13. Add the vanilla and salt and beat on low until fully incorporated.

14. Gradually mix in the powdered sugar and heavy cream on low speed. If too thick, add cream a teaspoon at a time. If too thin, add powdered sugar a quarter cup at a time.

15. Cover the frosting with plastic wrap until ready to use.

16. Once the cake is completely cool, flip it out and remove the flower nails, if used.

17. Spread an even layer of frosting over the top and swirl it with an offset spatula. Decorate as desired.

18. Cut into 30 squares with a sharp knife.