Preheat oven to 350°. Spray a 13x9-inch baking pan with baking spray with flour.
In a large bowl, whisk together flour, baking soda, pie spice, and ¾ teaspoon salt. In a medium bowl, whisk together eggs, oil, and sugars. Whisk egg mixture into flour mixture just until combined (a few streaks of flour should remain); fold in carrots and raisins. Spread batter into prepared pan.
Bake until a wooden pick inserted in center comes out clean, about 30 minutes. Let cool completely in pan on a wire rack.
In a large bowl, beat cream cheese, butter, vanilla, and remaining ¼ teaspoon salt with a mixer at medium speed until smooth. Gradually add confectioners’ sugar, beating until smooth. Spread cream cheese mixture onto cake. Garnish with walnuts, if desired. Cover and refrigerate for up to 3 days.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/carrot-sheet-cake-recipe/