How to Make It
Heat oven to 350° F. Butter two 8-inch round cake pans, line the bottoms with parchment, butter again, and dust with flour, tapping out the excess.
In a large bowl, whisk together the flour, sugar, baking soda, baking powder, pumpkin pie spice, and salt. Make a well in the center of the flour mixture. Place the butter, sour cream, and eggs in the well. Whisk together, then gradually incorporate the dry ingredients (the batter will be thick). Fold in the carrots, pecans, and raisins.
Transfer the batter to the prepared pans and bake, rotating pans halfway through, until a toothpick inserted in the center comes out clean, 40 to 45 minutes. Cool the cakes in the pans for 15 minutes, then turn out onto racks to cool completely.
Invert one of the cooled cakes on a serving plate and spread with 1 cup of the frosting. Top with the remaining cake. Spread the top and sides with the remaining frosting. Sprinkle with pecans.