Preheat the steamer by bringing the water in the steamer to a boil over medium-high heat. Cover the lid with a kitchen towel to catch the condensation.

In a medium bowl, combine all-purpose flour, baking soda, baking powder, salt, ground cinnamon, and ground nutmeg. Set aside.

Using a handheld or stand mixer fitted with a paddle or whisk attachment, whisk together eggs, granulated sugar, brown sugar, and vanilla extract until light and fluffy.

Whisk in the vegetable oil into the batter little by little until everything is well incorporated.

With a spatula, fold dry ingredients into the batter until well incorporated. Do not overmix.

Stir in grated carrot and raisins until well combined.

Pour the cake batter evenly between both prepared cake pans. Steam for 35-40 minutes or until a toothpick inserted into the center of each one comes out clean.

Remove from heat and allow carrot cake to cool in the pans for 10 minutes, then run a knife around the edge and invert onto a cooling rack to cool completely. The cakes must be completely cool before frosting and assembling.

In a large bowl using a handheld or stand mixer fitted with a whisk or paddle attachment, beat the cream cheese and butter together on medium-high speed until smooth.

Beat in milk, vanilla extract, and confectioners sugar well combined.

Level the tops of each cake with a knife or cake leveler. Place 1 cake layer on your cake stand or serving plate. Evenly cover the top with frosting. Top with 2nd layer and spread remaining frosting all over the top and sides. Decorate with toasted chopped walnuts or other toppings if desired.