Heat oven to 350°F. Grease bottom and sides of 13x9-inch pan with shortening or cooking spray; lightly flour.
In large bowl, beat granulated sugar, oil and eggs with electric mixer on low speed about 30 seconds or until blended. Add flour, cinnamon, baking soda, baking powder, 1 teaspoon vanilla and the salt; beat on low speed 1 minute. Stir in carrots and nuts. Pour into pan.
Bake 40 to 45 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour.
In medium bowl, beat cream cheese, butter, milk and 1 teaspoon vanilla with electric mixer on low speed until smooth. Gradually beat in powdered sugar, 1 cup at a time, on low speed until smooth and spreadable. Frost cake. Store covered in refrigerator.