Preheat oven to 350°F. Grease and flour one extra tall (at least 4 inches in height) 8 inch cake pan and set aside.
In a large bowl, combine the carrots, shredded coconut, brown sugar, vegetable oil, eggs, and vanilla extract.
In a separate bowl, combine the whole wheat pastry flour, baking powder, baking soda, cinnamon, ginger, nutmeg, and salt. Incorporate the dry ingredients into the wet, stirring until combined. Fold in raisins and chopped walnuts.
Pour batter into prepared pan. Bake for 35-40 minutes, until a knife inserted in the center of the cake comes out clean, then allow to cool completely before frosting.
To make the frosting, whip the butter and cream cheese until light and fluffy, about 3 minutes. Add in the vanilla extract, salt, and powdered sugar and whip to combine, about 2 minutes more.
Once cake has cooled, remove from pan and frost with frosting. Top with additional shredded coconut, and decorate with rosemary pieces.