To make the macadamia frosting, blend all ingredients in your blender (high speed preferably) until smooth, adding in some water as needed.
To make the cake, chop the carrots into small pieces and then throw into your food processor with the other cake ingredients and pulse until it's all in really small pieces and sticks together.
To assemble, put half of the cake mix into the bottom of a lined springform cake tin and press firmly with a spoon. Then spread on about 1/3 of the macadamia frosting. Then place into the freezer until the macadamia frosting is hard.
Then put the rest of the cake mix into the cake tin and press firmly with a spoon.
The put the remainder of the macadamia frosting into the cake tin and place back into the freezer until the frosting is hard.
When ready to serve, take out of the freezer and decorate with walnuts.
Serve and enjoy.