Position a rack in the middle of the oven. Preheat the oven to 350°F (180°C). Grease two 9-inch round cake pans, line the bottom with parchment paper, and then grease the top.

Whisk flour, baking soda, salt, and cinnamon in a medium bowl until very well blended.

In a separate bowl, whisk the oil, granulated sugar, brown sugar, and vanilla. Add the eggs, one at a time, whisking after each one.

Switch to a large rubber spatula. Scrape the sides and bottom of the bowl, then add the dry ingredients in three parts, gently stirring until they disappear and the batter is smooth. Stir in the carrots, nuts, and raisins.

Divide the cake batter between the prepared cake pans. Bake until the tops of the cake layers are springy when touched and when a toothpick inserted into the center of the cake comes out clean, 35 to 45 minutes.

Remove the cakes from the oven, and leave them in the pans for 15 minutes, then carefully turn the cake layers out onto cooling racks. Remove the parchment paper and cool completely before frosting.

In a medium bowl, whisk or sift together the cornstarch and powdered sugar. Set this aside.

In a large bowl, beat the cream cheese with a handheld mixer on medium speed until very smooth, whipped, and creamy, 1 to 2 minutes.

With the mixer on low speed, add the cornstarch and powdered sugar to the cream cheese, a heaped spoonful at a time, until thoroughly combined.

Pour in the cold heavy cream. Beat on medium to medium-high speed for 2 to 3 minutes or until the frosting is whipped and creamy.

When the cake layers are completely cool, frost the top of one cake layer and place the second cake layer on top. Add the remaining frosting to the top of the cake and use a butter knife or small spatula to swirl the frosting around.