Preheat oven to 180 C / Gas 4. Grease a 20x30cm or similar size baking tin. Set aside.
In a large bowl, mix together sugar, oil, eggs, vanilla and buttermilk. Stir in carrots, coconut and pineapple. In a separate bowl, combine flour, bicarbonate of soda, cinnamon and salt; gently stir into carrot mixture. Stir in chopped nuts. Spread batter into prepared tin.
Bake for 55 minutes or until skewer inserted into cake comes out clean. Remove from oven and set aside to cool.
In a medium mixing bowl, combine butter, cream cheese, vanilla and icing sugar. Blend until creamy. Ice cake while still in the tin.
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