Preheat the oven to 350 degrees Fahrenheit. Sift together all-purpose flour, baking soda, salt, and mixed spice into a bowl. Whisk, then set aside.

In a medium-large mixing bowl, add Hellmann's Mayonnaise, vegetable oil, sour cream, light brown sugar, and vanilla. Mix well. To loosen up the mixture, mix in whole milk.

Gradually incorporate the flour mixture into the wet mixture.

Add shredded carrots and walnuts. Mix well, then add the cake batter into at least 2 cake tins (8-inch or 9-inch as shown), and bake for 30-35 minutes.

Allow the cakes to cool in the tins for 15 minutes before turning them out onto wire racks to further cool until they are room temperature. (You can speed up this process in the refrigerator if low on time.)

While the cakes cool, make cream cheese frosting, Use a stand mixer or hand mixer to blend salted butter and cream cheese. Continue mixing while adding one cup at a time of powdered sugar and the vanilla. Mix until smooth.

To ice the cake, lay one of the 9-inch cakes on a cake stand and spread a generous layer of cream cheese frosting to fully cover the top, being careful to go past the perimeter of the cake. Layer the second cake on top, then use the remaining cream cheese frosting to cover the top and the sides of the cake with an offset spatula.

Optional: Further decorate the cake by using orange and green icing to make carrot-colored decorations, and sprinkle chopped walnuts on top.