Preheat oven to 350 degrees F.
In a large mixing bowl, whisk together brown sugar, granulated sugar, vanilla extract, eggs, milk, and vegetable oil until fully combined.
In a separate mixing bowl, whisk together flour, salt, baking powder, baking soda, and spices. Working in batches, stir the flour mixture into the wet ingredients until combined. Do not over mix.
Fold grated carrot, coconut, and half of the walnuts into the cake batter to evenly distribute.
Pour batter into a greased 9" x 13" baking pan, spreading edge to edge.
Bake in the oven for 35 to 40 minutes, or until the top is golden brown and a toothpick inserted the center of the cake comes out clean.
Once the cake is finished baking, set aside to fully cool before icing.
To make the frosting, beat together softened butter, cream cheese, vanilla extra and salt. Then, working one cup at a time, gradually beat in the powdered sugar until the frosting reaches the desired consistency.
Generously frost the top of the cake, and sprinkle the remaining chopped walnuts on top.
Enjoy!