1. Preheat oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan.2. In a large bowl, whisk together the dry ingredients: flour, baking soda, salt, cinnamon, and nutmeg.3. In a separate medium bowl, beat the sugar, vegetable oil, eggs, and vanilla extract until well combined.4. Pour the wet ingredients into the dry ingredients and mix on low speed until just combined.5. With a spatula, gently fold in the 3 cups of grated purple carrots (and optional nuts).6. Pour the batter into the prepared 9×13 pan and spread evenly.7. Bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean.8. Let the cake cool completely in the pan on a wire rack.9. To make the frosting: In a large bowl, beat the softened cream cheese and butter on medium-high speed until smooth.10. Add the powdered sugar and vanilla, mix on low until combined, then beat on medium-high for 3 minutes until light and fluffy.11. Spread the frosting evenly over the cooled cake.