Heat the oven to176C. Grease two 9-inch round cake pans and line the bottom with parchment paper then grease the top of the paper. Or, grease and flour the bottom and sides of both pans.
In a medium bowl, whisk flour, baking soda, salt, and the cinnamon until well blended.
In a separate bowl, whisk the oil, sugars, and vanilla. Whisk in eggs, one at a time, until combined.
Switch to a large rubber spatula. Scrape the sides and bottom of the bowl then add the dry ingredients in 3 parts, gently stirring until they disappear and the batter is smooth. Stir in the carrots, nuts, and raisins.
Divide the 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.
Cool cakes in pans for 15 minutes then turn out onto cooling racks, peel off parchment paper and cool completely. (If you find that a cake layer is stuck to the bottom of the pan, leave the cake pan upside down and allow gravity to do its thing).
In a large bowl, beat cream cheese with a handheld mixer on medium speed until creamy, about 1 minute.
Beat in the powdered sugar, a 1/4 cup at a time until fluffy. Pour in cream and beat on medium speed for 1 minute. Chill covered until ready to frost cake.
When the cake layers are completely cool, frost the top of one cake layer, place the other cake layer on top. Decoratively swirl the top of the cake with remaining frosting, leaving the sides unfrosted. Scatter nuts on top.