Shred the carrots on the large holes of a box grater or in a food processor fitted with the shredding disk. Do not substitute liquid buttermilk for the buttermilk powder. To ensure the proper spreading consistency for the frosting, use cold cream cheese. If your baked cake is of an uneven thickness, adjust the orientation of the layers as they are stacked to produce a level cake. Assembling this cake on a cardboard cake round trimmed to a 6 by 8-inch rectangle makes it easy to press the pecans onto the sides of the frosted cake.