Preheat oven to 350°F (175°C). Spray a 9x13 inch baking dish with cooking spray.
In a large bowl whisk together the flour, salt, cinnamon, baking powder and baking soda.
In another bowl add the sugar, eggs and vegetable oil. Whisk until it all comes together. Alternatively you could use your mixer.
Pour the dry ingredients into the wet ingredients and whisk everything until well combined.
Add the carrots and walnuts. Using a spatula mix everything together until the carrots and walnuts are well incorporated into the batter.
Pour the batter into the prepared baking dish.
Bake for 45 minutes to an hour or until a toothpick inserted in center comes out clean. Let the cake cool completely before frosting it.
While the cake is cooling, make the cream cheese frosting. In the bowl of your mixer, beat the cream cheese together with the butter, then add the vanilla extract and confectioners sugar, and continue beating until smooth. Refrigerate until ready to use.
Spread icing over cake. Sprinkle with walnuts.
Cut into squares. Refrigerate until ready to serve.