Preheat the oven to 190°C. Lightly grease or line a 22cm cake pan.
Beat the sugar, oil and eggs together for 5 minutes, until fluffy. Sift the dry ingredients together and add to the sugar mixture with the carrot, nuts, sultanas and pineapple. Mix together until combined and pour into the cake pan.
Bake for 1 hour and 15 minutes. Remove from oven and allow to cool.
Meanwhile, make the icing by placing all ingredients in a mixing bowl and beating together until the icing is light and fluffy. Ice the cooled cake and decorate with extra walnuts if desired.