Preheat the oven to 350 degrees.
Butter and flour two 9-inch cake pans. Set aside.
In a bowl, mix together the flour, baking powder, baking soda, salt and cinnamon. Mix and set aside.
In a large bowl, add the carrots, eggs, buttermilk, vanilla, sugar, and oil and mix well.
Fold the dry ingredients into the carrot mixture and mix until just combined.
Divide batter evenly between the pans and bake 30-38 minutes until a toothpick inserted in the center comes out clean.
Allow to cool in their pans 10 minutes then turn out onto wire racks to cool completely.
While the cake cools, make the frosting:
Beat the powdered sugar, butter, buttermilk powder, vanilla and salt together on low until smooth. Scrape down the bowl well, and with the mixer on medium add the cream cheese one piece at a time. Beat until smooth.