Preheat oven to 350 degrees and grease three 7 inch cake rounds. Then line with parchment. (Grease and line with parchment paper no matter the size of the cake pans.)
In a bowl, whisk together flour, baking powder, baking soda, spices, and salt. Then set aside.
In a separate large bowl or in the bowl of a stand mixer, vegetable oil and sugars. Blend for 2 minutes until well combined. Then add in the eggs one at a time. Lastly, add in the sour cream and beat one minute. Scrap the sides as needed.
Add flour mixture a little at a time. Then fold in the carrots.
Spread batter evenly into the pans and bake for 45 - 50 minutes or until a toothpick comes out clean. Insert it in the center to check for doneness.
Let the cakes cool on a wire rack for 10 minutes and then flip them over on a plate to remove them from the pans. Cool completely on the wire rack before frosting.
To make the frosting, combine all the ingredients in a bowl and blend well with a hand mixer.
When the cake is ready to be frosted, trim the tops so they are flat. Frost as desired between the layers and around the cake.
Garnish and serve!