Preheat the oven to 350 degrees. Grease and flour a 9 x 13 inch baking pan and set aside.

In a bowl, whisk together the flour, cinnamon, baking soda, baking powder, and salt. Stir in the grated carrots until they're well coated.

In the bowl of an electric mixer, beat the sugar and oil on medium speed until smooth and creamy. Add the eggs, one at a time, beating well after each addition. Slowly beat in the pineapple.

Pour the carrot and flour mixture into the egg mixture and beat on low speed until combined.

Pour the batter into the prepared pan and bake for 45-55 minutes, or until a toothpick inserted in the center comes out clean and is no longer jiggly in the center. Allow the cake to cool before frosting.

Beat together the cream cheese and butter until smooth. Add the powdered sugar, one cup at a time, and beat until smooth. Beat in the vanilla extract and 1 Tablespoon of milk. If the frosting is still a little thicker than you'd like, add more milk, a Tablespoon at a time, until it's easily spreadable.

Spread frosting on the cooled cake. Top with nuts, if desired.