1. Adjust oven racks to center and upper third of oven. Heat oven to 350 degree F. Grease three 9-inch round cake pans. Line bottom of pans with waxed paper; grease and flour paper, tapping out excess. Set aside.
2. Arrange raisins in a strainer set over shallow water in a medium saucepan. Cover and bring water to boil; steam raisins 10 minutes. Set raisins aside.
3. Combine flour, cocoa, baking powder, cinnamon, baking soda, and salt in a large mixer bowl. Beat eggs in a large bowl on medium speed of electric mixer until blended. Beat in vanilla, granulated and dark brown sugars, and oil until well combined. At low speed, add flour mixture and beat just until blended. Stir in carrots, raisins, and nuts. Divide and spoon batter into prepared pans. Place 2 pans on 1 oven rack and 1 pan in the center of the other rack. Bake until tops of cakes spring back and edges just begin to pull away from side of pans, 35 to 40 minutes. Cool cakes in pans on wire racks 10 minutes. Unmold layers, remove paper and invert again onto racks; cool. Freeze layers 1 hour, until firm.
4. For frosting, beat cream cheese and butter in large bowl on medium-high speed of electric until smooth. At low speed, beat in vanilla and confectioners' sugar, until well combined. Increase speed to high and beat until mixture is smooth.
5. Transfer 1 layer to a large serving plate; spread top with one third of the Frosting. Repeat with remaining layers and frosting. Store, covered, in refrigerator. Makes 12 servings.